Willingness to not respond to my Cancellation requ

I have been a netstar customer for over 8 years, I am tired of poor service and lack of assistance. I have been double billed numerous times and getting my money bakc was always a problem so i canceled my debit order and pay cash. They then stopped sending me invoices after which i would request they send me one EVERY MONTH so i could make payment as i will not do so without one. The only feedback or comms i get from Nedstar is when they want my money, BUT THEY STILL CANT SEND ME A BILL. I have requested numerous times for a bill and numerous times for the cancellation amount so i can cancel with them and move to another provider. It has been over a week and still no feedback but i an still getting the SMS to PAY. PLEASE can someone help me terminate both my netstar contracts