Sent to collections after cancelling

I cancelled my service in October of 2022. I returned the router within the allotted time period. Today I got an email from a collection's agency called Sequium with a reference number. The email was a former roommate's name on it. The level of incompetency here is unbelievable. I spent half an hour earlier today in a chat where the agent promised to send the follow up email with a billing manager, and it never came. I just spent another hour on the chat and they disconnected on me after I warned them that their responses were coming through slowly.

None of the agents has any clue what they are talking about. The last guy was about to refund me $95 and asking for my payment information, for some inexplicable reason.

This is absolutely unacceptable. Please respond quickly, and please make sure the person who responds has the ability to understand what I'm describing, work with the collections agency to reverse this, and provide me and my former roommate detailed information about how this happened and how the situation is going to be corrected.