incorrect billing

I did a premature cancellation for my two contracts on the 28 April 2017 and i paid R2 980.02 to cancel both contracts but they were not cancelled in june 2017 the contract were opened . in Sept 17 vodacom called me to say i owe them i said it cant be because vodacom wanted to correct the error they cancelled the contract and they said i must pay R390 in December 17 I paid R400 but now they are saying i owe R2 200 I dont have that money and i wont pay it because they said the R2 980.02 I paid in April 17 was enough to cancel both contract now i cant evem buy a new phone