Paid account

I changed my bank account type in the beginning of this month. Went to MTN in Paarl twice to request them to change the account. 2nd of December they deducted from my old account that had no money in. Paid the balance on the 8th of December and put wrong reference number in (my fault). Called the call centre(very patient helpers) more that a couple of times.In middle of December they cut off my service because MTN said I didn't pay my account.Sent my proof of payment and a few days later I got two sms's informing me that they are reactivating my services. Called them again and they put my services back on. Got a sms this morning (30th December 2015) telling me they will be debiting me R489 and some odd cents. That includes the so called amount I did not pay (BUT I HAD) counting the total statements that proved that I paid my account equals to 3 . I cannot begin to express the amount of frustration I experienced (still am) . I changed from Vodacom to join MTN. I made a huge mistake. MTN still has to credit me money from the beginning of the year that they wrongfully deducted after another contract was already closed! This is really the worst service experience.