Cell C ***** contract

Two months ago cell c contacted me and they informed me that someone must have opened a contract in my name using my ID number. I confirmed to them that it was not me and and asked me to send the affidavit showing that I didn't open the contract. They only informed me because the debit order didn't go through in my bank account so they wanted to know why. I submitted the affidavit along with my copy of my ID, but I still get a call from debt collectors regarding that ***** account. I thought they were going to settle the matter.