Service cancelled but billing continues

My dad stopped all rain services about 2 months ago due to the promised speeds not being delivered, yet to this day he's still getting billed. Their support function on the website doesn't work, as clicking Submit does nothing. A number of emails have been sent to them since the 14th of May this year to cancel the debit orders but all we receive are automated messages with reference numbers. There's not even a contact number that one can use to speak to someone in order to discuss resolution of the issue. My dad is a pensioner, and he can't afford to keep getting billed for a service he's not receiving. Please help.