Mix Telematrix Cancellation nightmare

I called Matrix in September 2021 asking them to help me cancel my subscription, the agent told me that she cannot help me cancel if i have not sent a cancellation email first. She gave me the email address and immediately sent the cancellation email, i never got any response, i stopped paying in November because after trying to contact them for the umpteenth time and getting no response, i was fed up. I no longer need their service, but cancelling is a nightmare! Now they keep sending threats to list me for non-payment, am I stuck with them for eternity? Still when i call i cannot get through because of high call volumes, I am helluva gatvol at this point!