Formal complaint against your collections agents

I have received calls from vvm attorneys for mtn. These agents are very unprofessional and they hung up on me 4 tyms already. I wish to have this matter investigated by mtn as they call on your behalf. Please requested all call recordings and contact me as this is appalling service from a so called attorneys. I was called the first time by a lady who spoke to me as if I was her friend and then she spoke rudely to me. The next agent hung up on me when I told them what happened previously. The last call I received a few days ago, I requested to speak to a manager and they hung up on me. I would like someone with authority to contact me