Phone number changes are free except when they are done within the same location due to a dislike for the number itself (then the cost is $10); if you are changing your number because you’ve moved or you are being harassed by audio or text, then it is free.

"Moving" would be a different area code or province. Proof may be required... I don't know.

You could try the "harassed" excuse, but since they will have access to logs of incoming calls and texts (probably not the content, but a count of how many), you'd better have proof of dozens or hundreds of unwanted calls/texts.

All that's left is "I don't like this number", so..... $10.
And no, you don't get to pick a number you "like".
Probably $10 more every time after that, or an outright refusal to change it any more. Do it too many times, or too often, and they will likely assume YOU are the one doing the harassing, and cancel your account.