You cannot select a different collection agency.
However, the two most important rules are:
1) Never, ever speak to them on the phone, for any reason whatsoever. Communicate only in writing, never on the phone. Do not call them. If they call you, hang up, without even saying one word. Once you say anything, even just hello, to any collection agency, you give them the ability to lie about what you said.
2) Do not give them your bank account number, because they can use it to take more money that you authorized. Pay with a money order instead.