Cancelled contract after 24 months and now been harassed by debt collectors...

I cancelled my contract around the 8th or 9th August 2017 and since Friday, 25th August 2017 I have been harassed by a debt collection service.

Doesn't MRPmobile take a last debit order like the other mobile services? and if this was not the case, why wasn't I informed that I needed to make one last payment?

I have received no communication from MRPmobile since cancelling my contract nor have I received an invoice for payment.

This is not the type of service I expected from MRPmobile and I have never been treated like this by any other service provider, bank or shop!