Handed over to debt collectors for paid up contract that has been terminated

You have pathetic service- I terminated my month to month contract more than a year and a half ago (which was paid up) and you have collected your router. I received and sms yesterday saying I’ve been handed over to Easton Berry Debt Collectors. After calling your support line and being put on hold 3 times a spoke to a gentleman raising my concerns and asking for an email proving I’d cancelled it - his response was the team did not cancel it when I requested it but only later - how is that my problem because you pay month to month ?? You better sort this out and clear my name- I definitely would warn anyone not to use your service!!!