Call centre so useless

For months now i am struggling to resolve an account query on my account.

When my balance owing goes down my instalment due goes up.

Example: NOVEMBER 2017 statement Balance was R3236 and Instalment was R468.

I also paid extra with total paid being R470.

DECEMBER 2017 statement Balance was R2928 and Instalment was R614

Your call centre cannot seem to help me. Yesterday I went to Jet Brixton and a lady by the name of Naninke assisted ( She was so friendly and helpful) She than called Customer Care from the store and i spoke to a call centre agent after being on hold for 10 minutes she drops the call.

We call again and speak to a KHANYI who told me she does not know whats wrong and there is no senior on duty she will call me back on the 16th December 2017. No call.

Can someone with the knowledge and customer care s****s help me.

I also want KHANYI to call me back and apologies for her lies.