Service Suspended

My services were suspended today because i was told to pay R314.04 that i don't even know where it comes from. I received an sms on the 25th of September 2015 that my account will be debited with R937.64. On the same day i received a statement saying about the amount to be paid which is R625.84. I called mtn to find out why the two amounts differ yet i received notification on the same day. They could not tell me where the R311.80 difference come from. I went to mtn Springs and Khaya checked for me but still he couldn't explain to me what is happening, instead he told me to pay the amount on my statement. I asked him to cancel the debit order and I made the payment of R635. On the 19th October 2015 i get an sms that i need to pay R314.04 or my services will be suspended. Today my services are suspended still without any explanation why i need to pay R314.04 and where it comes from. I called mtn and the lady i was talking to said that i have an outstanding of R302, she doesn't know about R314.04 but still couldn't tell me where it comes from. She said i need to call mtn collection maybe they will assist me. If this carries on, i will move my contract to CellC, can't go on like this.