Hello fibre continuously overcharging and not sticking to the contract

Every month I have been overcharged on my telling fibre account. Every month I have to call in to rectify the charges . For the past 3 months I have been overcharged again can this permanently be rectified? I signed a contract on a specific plan and price why is that not being honoured why is the cost higher every month. Telkom are in breech of their own contract with me. Please offer a permanent solution ASAP. I have been a loyal customer for so many years even through the numerous hiccups experienced