Incorrect installments charged

Last year 2019 end of July I took a contract phone with vodacom in Greenstone. I went there to get a cheaper phone where I will be paying less instalments. However I took P30 lite which on the contract said its R279 however I was billed R295 every month up until I decided to end the contract by settling the remaining balance. Last week I was going through my things since I relocated from gauteng to limpopo last year September and only to find the contract that I signed for R279 which I was paying R295. I then decided to call vodacom Greenstone and I spoke to the lady called Nelly who was rude. She told me that I must call the call centre, they will explain to me why I was charged that or it's either I come to their store. I told her that the reason why I called the store is because I'm no longer in Gauteng & I got the contract in the store & not the call centre. She then said to me that's how they do things, she won't be able to help me as the store is busy because of month end. What kind of service is that? When they were looking for the sales that time that I took a contract with them, I was important and now that I want to complain she can't assist me. I asked for a supervisor and I was told they are all busy. She just left me on the phone, and I can hear from her background that she is attending someone. I want the difference that I was paying monthly.