Sport Direct chasing me for money! Again!

Hello,
I'm being chased by CRS (debt collection) for a total of £44. They were handed my case for collection of £8 for a gym membership i had two years ago and have added their £36 charge.

However two years ago i had the same situation with Harlands (CRS' previous name) where they chased me for payment owed to Sports Direct gym totalling £36.
I happily paid a total of £8 per month until the debt was cleared, however what i didn't read on their confirmation of payment plan letter, was that unless i stated otherwise they would keep my account open and continue to take the payment for membership, even though i told the man over the phone that i wanted to cancel my account.
I cancelled the direct debit from my bank account, unbeknown to me that my membership was still running. However received a number of emails after asking me to join their gym again.

So two years later they are now requesting money from me that i didn't know that i owed, even though they had my email address, which is how they found me as my address had changed.

I am totally confused as to whether i have any rights to dispute this and completely baffled as to why this has happened. I know it is a small amount to pay but they've caused a lot of stress on my part.

Any advice?