DSTV harassment via debt collectors Blake and Associates. I owe zero!

I am constantly being harassed by debt collectors appointed by DSTV called “Blake and Associates”. I do not owe anything too DSTV. Their billing department has confirmed this. They call my cell and hang up, and they phone my home... for weeks on end. I do not owe anything and they are asking for proof of payment for the amount they believe is due. DSTV cannot stop this, even though the problem is apparently escalated in their billing department. This is completely unacceptable. Please help me!