Send them a letter via CMRRR stating that you are rescinding consent to calling your cell phone. If you want to cover all the bases, list the cell phone number(s) you are no longer wanting them to call. That way they can't claim they didn't know which number(s) they are no longer allowed to call.
"Send them a letter via CMRRR stating that you are rescinding consent to calling your cell phone"
Now, what if you never gave them consent to call your pay as you go cell phone in the first place?
For example, say you got the pay as you go cell phone years after the credit cards went into default, and so the pay as you go cell phone number was never on any application and you personally never called the creditor or junk debt buyer or collection agency from your new cell phone, and you never gave them your new number.
Couldn't you just send them a letter which says that you never gave them any authorization or permission to call your cell phone, and that you demand they never call your cell phone number again?