Mswipe Technologies — Swipe machine cancellation

I signed up for an Mswipe Mobile POS solution in November, 2016 to use for an event. After the event completed in December 2016, I called their customer care and asked them to cancel my account.
The customer care executive informed me that they would have someone contact me to take the matter forward. No one came at the time, and due to complete non-usage of the machine (records can be checked) I forgot about this.
Now in 2021 I'm suddenly getting calls from their thuggish customer care executives demanding I pay the pending monthly charges accruing since then. They have been calling me non-stop and even tried to waive off the amount.
Apparently the cancellation requires some paper from them, but how am I supposed to know this? Should your customer care not have informed me at least that more steps are required? Why make claims to handle it and then forget it and then try to blame the customer?

The amount aside, the attitude of their customer care is terrible. Why was such action not taken once I submitted my cancellation request? Why was there no follow up then? Why should I pay for a machine I cancelled and have not used in the last 4 years?

Signing up with them was a big mistake that I still seem to be paying for now. I want this harassment to stop immediately. I don't use your machine at all and you may send someone to retrieve it, but I will not pay for charges based on your company's incapacity to do it's job.