How did my card get used without my permission?

Question

I got my money back – this question is about the mechanics of how they got my money in the first place?

How did my gym spend my money?

I signed up to martial arts classes at Tribe Gym.

I paid using my debit card.

I only went to the classes 4 times (4 weeks).

A few weeks later, I saw a transaction on my statement – someone bought a snack for £2 at the gym at around 1am.

It was impossible that it was me – by then I had stopped going to the gym for weeks and the gym was closed because of covid.

In the end I got the £2 back, but I’m not curious about HOW they were able to spend my money?

My debit card was at home with me when this happened.

In: Technology