Poorest Customer Service Ever - Supersonic Fibre

Supersonic customer service have no clue on how resolve accounts issues. I app**** for a 10mbps fibre line, one month they do not take any money and the next month they just take two months payment whithout any notification. Approx 3 months into my contract they suddenly charge me for a 20mbps line without me knowing or requesting this and my line at home is still on 10mbps. After several phone calls and emails they acknowledge that I have a 10mbps line but they do not know why they charge me for 20mbps and that they will correct it.. After several calls and two months they still have not resolve the issue and they still charge me for a 20mbps line! I emailed them to cancel my contract. It is now 2 weeks and no came back to me to acknowledge my request to cancel or to call me to resolve the issue or anything.... It is the worst service provider I ever dealt with.