Debt Collector harrastment

I had a tracker device with Altech in 2012, My car was involved in an accident October 2013 and was written off in December 2013 if not early November. I paid my tracker monthly through debit orders.

The past year (late 2019) I have been getting messages and calls from a debt collector advising that I have an outstanding amount on my Altech account that I owe, I contacted Altech questioning what is this about and why it took the more that 5 years to contact me, they advised they will get back to me, to this day they haven't and I am still getting messages about me owing them.