Supersonic after sales not good at all

For 4 months I have been struggling to sort out my incorrect billing frim Supersonic. I relocated in July 2021 to a new address and asked Supersonic to transfer my fibre line to the new premises and to disconnect the old one. They promised to do so but never disconnected the old fibre line. Eversince, I am billed for both fibrelines and through all my attempts with them to rectify their negligence I still have no joy and now they expect me to pay the line that is no longer in use. If I dont get get this sorted out today, I have no choice but to take this matter to higher authorities. Supersonic is good in making promises when they recruit new customers but the after service is poor.