Home cloud WiFi

This company advertisers month to month deals that's the only reason I went with them... The Telekom lines were always down and I never had good signal on my Wi-Fi, hence after about 6 months I wrote to give my months notice and was told it's a contract and I cannot cancel. Since then they do nothing but harras me for money owing to them and refuse to cancel my debit ordet every month I have to go to the bank to reverse the payment... False advertising!!!!!! Harassment!!! Bad credit record as well now. What to do???