letter of demand and **** allegations

After numerous attempts and proof that i should not have been handed over to them or have a balance owing for that matter, i keep getting emails that i need to pay and it has escalated where i am being issued a final demand. I signed up for a month to month contract with rain and i stopped using rain because i found a new offer elsewhere. it was brought to my attention when i checked my spam folder on my Gmail and found that Nudebt has been sending me emails which i never noticed were coming in. what made me more angry Nudebt claim to have called me and i agreed to pay them on certain date of which i never received a call from Nudebt.