Unfair unreasonable service

I was a member of Monitor Net for 11 years during which time I was very happy with their service. Unfortunately my alarm system broke and I could not afford a new system. I told the person from Monitor Net who gave me the quote that I can unfortunately not replace the system and will have to gave up my membership eith them. At no stage did he inform ne that I must fill in a cancellation form and give a month notice. I stopped paying but kept on receiving invoices. I advised them every month that I can no longer use them as I no longer have an alarm system. Again nobody told me that I must fill in a cancellation form. Now a year later they are giving me over to an attorney to collect almost a year's subscription for a service I could not use. I explained many many times what happened and they asked me to provide evidence that I told the person who gave me the quote that I cannot continue with membership. I explained to them that the email communication was on my work email and as I retired end of December 2021 I no longer have access to that emails. I requested them to check on their side but they are not willing to do that. In addition they are billing me for a radio transmitter which they removed themselves. I paid faithfully for 11 years. Why am I liable for a service I could not use and for components they have removed? They are not reasonable and fair.