MTN Contract!

I have a phone contract with MTN and the agreement based on my contract is they debit on the 25th of every month it’s been almost 7 months now with the phone . They either email me , send me Sms about payment reminder and I end up going to pay at the store. Recently I went to the store to get this fixed and I paid cash after a few days they debited and when I called they directed me to the bank instead of fixing their system. Last month they didn’t debit and this month I got a billing of 1800 and I went to the store AGAIN! They insisted it’s solved! I paid the money on EFT as the lady who was assisting me said they won’t be able to debit this month just right after I paid they debited again ! Mind you it’s not even the 25th . I’ve never had just bad experience as this! I’ve just called the branch and the manager just asked me why did I pay?!