*********** service provider MTN unable to bill correctly and debiting money incorrectly

This is an ongoing saga from November 2018. I have been double debitted by MTN since Nov 18 to April 18 , thats 5 months of being charged R809 instead of R400. MTN the ******* that they are, are now only willing to credit me R1432.88 , instead of a full R2400. I am sick and tired of an *********** billing team who has taken 2 months to explain to me how they came to R1400?? And why am i getting a credit on an MTN account when MTN has incorrectly debitted my banking account - how is that fair? Do I work for MTN to help themselves? I even have it on email that they have been charging me for an additional line, but now they only want to credit data. Its the most disgusting, unhelpful, useless network ever. And absolutely no one has an idea of what they are doing. What must i do with your apologies, does it put the money back in my account? I WANT MY FULL AMOUNT BACK MTN - I AM FED UP OF YOUR PATHETIC EXCUSE FOR SERVICE; AND I WANT A CREDIT INVOICE FOR THE FULL R2400.