Poor Service

Firstly I have been paying Telkom via EFT because I have issues with my bank for unauthorized debit orders I called Telkom to enquire if I could change my debit order date I wasn't assisted... I viewed my bill to check if they received my payment and they did. But to my surprise my February bill is R531.50 it includes a bill I'm not aware of a once off of which I'm aware I paid for it in October when I took the contract. I need an explanation or Better yet a settlement letter to settle this account before it gives me problems cause I took it to boost my credit score not to damage it.