Harassment and mistreatment

FNB handed over my account to Hammond Pole when I had not skipped any payment for my credit card. I am being harassed by this company and they are telling me that I have not paid even after I sent proof of payment. Receiving random calls and people keeping quite on the phone. Even after trying to negotiate a settlement you open yourself for further harassment. No meaningful help.. ************** from FNB and Hammond Pole