Incorrect billing and unable to rectify

My bill with Vodacom was outstanding in October with R800, and I had not been receiving invoices or statements.. I phoned and paid half the value; bringing my balance to R400, my monthly charge on the line with handset is R200, I have my old initial invoices... So R400 + (R200 x 3) = R1000 owed in Jan to settle and my contract ends in February.

I receive a final letter of demand for R3630.98 on my same account. I phone the call centre, no one can answer me.. I should call back?

What level of service is this to be handed over so easily based on improper records and no one who is able to validate the information and telling me to call back?

I must just sit here and pay?

Vodacom, please rectify this or reach out to me or I will be taking this further. This is ***** at best.