Messing up my credit score

I've tried to call these guys multiple times to cancel my account with no luck! I even made a request on the app for a call back but still nothing. I received a statement that says that I owe them, and this is because I stopped the debit order from my bank account! I called again today and was transferred to their cancelations department but I held until my airtime was finished. This is going to negatively affect my credit score and it's not even my fault!