Kindly help me get a refund

Greetings to whom it may concern! ****!

I have a contract with MTN , these past months I couldn’t pay the contract unfortunately they had to black list me , they then sold my contract to the lawyers then I was placed on the legal team. Surprisingly on Saturday the third-party deducted R1800 on my account without my concern . It shows that I paid with cash but they deducted my money via EFT without my concern/ permission