Poor Service MTN LTE internet: I am being charged twice

I have purchased an MTN LTE home internet via the MTN website and the end of July, I was request by MTN to make an online payment, which I did which include my pro-rata fees. I than got debit the same amount a few Days later, I rejected the debit, reason being I just made the payment onliine via eft a few days earlier. I than called mtn and spoke to an agent, she asked me to send through proof of payment via email, which I did. I received confirmation via email hat the payment was allocated. Now I received my invoice for the month and my payment as not been allocated and I am being charged again for my initial fee which has already been paid. I called the mtn customer care again today I spoke to an agent, she says I must send an email to customer to allocate my payment. Why must this process be repeated. I only get a response from an agent in 2 or 3days lateer.

No one seems to be sorting this issue out. This is such poor service from MTN.