Worth complaining about lost credit (UK)

In September 2025, I attended a private pelvic physio appointment and booked a follow up. Due to a medical emergency I cancelled the follow up and was told they would reach out to talk next steps. The medical emergency was related to the physio - not their fault but they likely worsened something.

I never heard from them and wasn’t in a place to get in contact for a while. I’ve put off getting in contact as it was very traumatic - not sure I’d want to be treated there again even though nothing was their fault.

I rang in June to ask if I could have a refund for my credit or use a different service. Was told that credit only lasted six months and was therefore lost. I verbally accepted this but now feel I should have pushed back. There is nothing on my receipt about credit limits, can’t find anything on their website and nothing was said to me when I called to cancel. No warning email or call about credit. Promised telephone follow up didn’t happen.

Is it worth complaining?