Cancelling because of bad service, byt cancellation service even WORSE.

After 2 months of terrible service on my ADSL in December in January, I decided to cancel my landline and ADSL ***) I sent the first request to cancel the line on 3 Feb 2016, and numerous times after this. I still get billed every month, and they have now started to send SMS's to threaten me. I have phoned numerous times, tried to speak to supervisors, but get cut off everytime they tell me they are putting me through to a supervisor. I wanted to cancel because of bad service, and now the service is event worse trying to cancel.