Worst possible service ever!

One of my accounts was handed over to this company for collections. HTN Attorneys contacted me to make a payment on the account, offering a discount on the settlement of the account. The discount was valid for a limited time only, until Dec 31 to be exact. The sent me an sms to confirm the banking details and amount that I had to pay together with an email address to send the proof of payment to. I did all of that on the 20th of Dec, I scanned and email the proof of payment on the following Monday, Dec 22. <br> To my surprise, 3 months later I get sms notifications to pay the same account that I paid in Dec. I have made countless calls and emails to HTN Attorneys to get this issue resolved and each time their response has been \We will investigate and call you back"or \""my manager is busy on another call and they will call you back as soon as they are done\"". In the meantime"