Being overcharged on my Business line since 2019 ***

Last year i app**** for a 20 MB ADSL line that costs R1099 (Mentioned clearly on their website). However, after receiving the line i was being overcharged R600-R800 every month and as their service is ridiculously bad it took me a while to register a complaint with the billing department (12th March 2020) with the reference ***4. I never received any feedback from Telkom and they rejected my complaint without any reason. I called the billing department again for rejection reasons and they informed me they can't assist me as they don't know what kind of contract i signed??????? The most ridiculous comment ever heard from a company. FIX MY PROBLEM OR CANCEL MY LINE!!!!!!!!!!!!!!!