Invoices sent through from 2015 with 10 days notice to pay before disconnection!

I've been with IS Ignite (Internet Solutions) for nearly four years and until this week I had nothing but good things to say about them. That is until I received an email with copy invoices dating from Jan 2015-Sep 2015 telling me I had 5 unpaid invoices and if the account balance wasn't cleared by 1st Sept my account will be disconnected. The invoices relate to a period when I was paying by credit card so was totally confused. Each month they would send me an invoice, automatically debit my credit card and then send a confirmation email to say the Invoice had been approved and the account activated. It turns out they had a problem with their credit card payment system and although they were confirming payment had been taken, they never actually debited my card. Now, more than two years later they want full payment for their error, which they admit is their error, otherwise they'll disconnect my service, despite the fact I've been a loyal customer for nearly four years who hadn't missed a payment (as far as I was aware), and have given me less than 10 days notice about all of this. Totally disgusted and already looking for alternative internet supplier.