Is it worth replying to Xercise4less to refuse their offer and reiterate that I am willing to pay the £14.99 months membership but nothing else?

I have been having issues with the cancellation of my Xercise for less membership. I completed the online cancellation form on 14th November 2017. At the same time, I cancelled the DD with my bank. I realise now that they do state on their cancallation form that you must give 30 days notive, so in hindsight I did cancel my direct debit too early. After this date, I started to recived email/txt/letters stating that I owed money. I initially read some posts on this webpage and I ignored the correspondance. It went through the usual form: Harlands adding admin fee / CRS txting saying they need to speak to me urgently. I noticed that each correondance from CRS was getting higher in the amount owed. Finally landing at around £180. I decided to try and sort it with Xercise for less. I spoke to them on the phone last week. They saif they could reduce the pice to about £60, which was for my months membership that I didn't give notice for and the buy back fee for the dbt off CRS. They said that would "stop me getting issues with my credit rating, and make it all like it never even happened". I refused, I told them I would accept the £14.99 1 month membership for cancelling my DD too soon but I will not pay anything extra. I also asked why, if they received my cancellation reques form, did they ignore it and coninue to rack up dept on my account. He said because I did not follow the terms of cancellation and cancelled my own DD. I then sent an email (copied in parts from one I saw Slick write on here) about my change of address - as letteres went to my old one - and also regarding the nature of the intimidating letters. I reiterated that I would pay 1 month membership and nothing else. I recieved a phone call a few days later which I ignored and emailed them to tell me to put anything they have to say in an email to me. I have now received an email to say that as a good will gesture they will remove all CRS charges, however as I did not update my address upon relocating they will charge me a £25 admin fee plus my £14.99 outstanding membership payment. So £39.99. Should I refuse this? - also, I moved house AFTER I submitted my cancellation form so it is irrelevant to them where I live at that point. Any advice I what I should reply to them with would be very much appreciated. Thanks