A better approach would be to use generators to calculate the next humble number, using the information that the next number has to be next multiple of 2, 3, 5, or 7 compared to a previous humble number. Various approaches exists to do this, amongst them the one in Barrys answer (which got written while I write this answer), or the one suggests from Martin R from Rosetta code related to Hamming numbers.

If you exchange Rosetta Code's hamming() (Cyclic generator #2) with the following you'll get a quite fast version:

A better approach would be to use generators to calculate the next humble number, using the information that the next number has to be next multiple of 2, 3, 5, or 7 compared to a previous humble number. Various approaches exists to do this, amongst them the one in Barrys answer (which got written while I write this answer), or the one suggested by Martin R from Rosetta code related to Hamming numbers.

If you incorporate the Rosetta Code's "Cyclic generator method #2" from link above, and replace the hamming() function with the the following you'll get a quite fast version:

Do however note that I don't recommed the variable naming, and the lack of comments on this code. According to Rosetta code this should be faster than a version based on heapq.merge, but I currently don't have time to run time verification on that.

• Choose better names – According to python style guide, PEP8, you should use snake_case for variables and functions. In addition what does dp, acc stand for? And in general one should avoid single letter variables except in tight loops
• Uncomfortable while loop – I'm a little confused by the loop in humbleNumber, you have loop using i and n, but mostly you focus and increment on curr. This doesn't read good, and is somewhat confusing.
• Anti-pattern of if True: variable = True – Setting a variable to True or False after you just checked it in an if statement, is kind of an anti-pattern. Normally you should rather do dp[curr] = ishumble[curr, dp). In your code this does require some other changes as well. See code refactor below
• Add spaces after commas – Don't clamp up list like in [2,3,5,7], add spaces around operations and after commas. It is better with [2, 3, 5, 7] and ishumble(x, dp) and so on
• Comment your code – Add docstrings to your functions, and comment before non-intuitive code segments
• BUG: ishumble(x/i) is missing the dp parameter – When testing a slightly modification of your code, I actually got to call the line which you comment that you don't get called, and it fails as it hasn't gotten enough parameters! (So yes, it doesn't get called in your version, and no, it doesn't work!)

def humble_number(n):
    """Return n'th number divisble only by 2, 3, 5 and 7."""

    humble_numbers = {}
    i, humble_candidate = 0, 0
    
    while i < n:
        
        # Find next humble number
        while True:
            humble_candidate += 1
            humble_numbers[humble_candidate] = ishumble(humble_candidate, humble_numbers)
            
            if humble_numbers[humble_candidate]:
                break

        i += 1
        
    return humble_candidate

• Choose better names – According to python style guide, PEP8, you should use snake_case for variables and functions. In addition what does dp, acc stand for? And in general one should avoid single letter variables except in tight loops
• Uncomfortable while loop – I'm a little confused by the loop in humbleNumber, you have loop using i < n, but mostly you focus and increment on curr. This doesn't read good, and is somewhat confusing.
• Anti-pattern of if True: variable = True – Setting a variable to True or False after you just checked it in an if statement, is kind of an anti-pattern. Normally you should rather do dp[curr] = ishumble[curr, dp). In your code this does require some other changes as well. See code refactor below
• Add spaces after commas – Don't clamp up list like in [2,3,5,7], add spaces around operations and after commas. It is better with [2, 3, 5, 7] and ishumble(x, dp) and so on
• Comment your code – Add docstrings to your functions, and comment before non-intuitive code segments
• BUG: ishumble(x/i) is missing the dp parameter – When testing a slightly modification of your code, I actually got to call the line which you comment that you don't get called, and it fails as it hasn't gotten enough parameters! (So yes, it doesn't get called in your version, and no, it doesn't work!)

def humble_number(n):
    """Return n'th number divisble only by 2, 3, 5 and 7."""

    humble_numbers = {}
    i, candidate = 0, 0
    
    while i < n:
        
        # Find next humble number
        while True:
            candidate += 1
            humble_numbers[candidate] = ishumble(candidate, humble_numbers)
            
            if humble_numbers[candidate]:
                break

        i += 1
        
    return candidate