Wrong Person, Stop Calling

Horrible experience, I'm being harassed regularly for an FNB debt that isn't mine. I requested the contract and was supp**** with a document that doesn't have my name, number or id number listed, It's someone else's and they still persist on hounding me for this account. Sent emails, made calls, they acknowledge that they got the wrong person in emails and over the tel, but the calls and sms wont stop.