MTN poor service and employees negligence

I had made double payment in one month in December and before I made the payment at branch I asked the person who was assisting me if on the 25th they won’t debit the money she said yes then I proceeded with paying but to my surprise they debit on the 25 while I had asked before making the payment, but instead of them refunding my money, they blocking my phone and saying I owe them. I have been making calls and follow ups I’m not getting the same answers everyday I’m getting a different explanation. I went to the beach to get a better assistance but still they told me they will call me back once they get feedback from the back office but they never call I had to call them and ask I even went to the branch again. Now my MTN account is seating on arrears I don’t know why because they are the ones who are owing me. And now on my bill it shows that I need to pay for two months and I have good mind that they will debit a double amount. At this point I feel harassed by MTN and their customer service is very poor they should also take their employees for training they need to learn basic skills! I have a good mind to return this stupid phone back to them because they keep blocking it I’m not getting any joy with MTN. I regret opening a contract with them.