Received extranormous account

After being switched from Nashua Mobile to M T N Data bundle. My data were switched off several times. I have been with Nashua Mobile for many years and never had problems. But when I phoned M T N 808 number they told me that I have Exceled my limit of R 128. At the beginning of February my data was turned off again. After phoning they told me that they have problems with their network and I will only get a statement on the 15th of the month. But I received a statement on the 12th of February by e.mail. ( After I bought a 8 ta bundle just to carry on with my business). What a surprise to get a Invoice for the amount of R 7476.55.. They call it \packet switched". On the 19th February I went to the M T N office. They told me to cancel my debit order to make sure it will not be taken off my account. The bank told me that there is only R 137 that will go off my account. But on the 27th Feb. an amount of R 7476.55 went off my account. What shall I do to get this back?"""