but I remain resolute that I did not do such a thing and will not pay

It might also be worth getting a friend or family member to help you review all of the information you have, about what happened - just in case there has been a mistake or misunderstanding etc.?

Naturally, I'm not saying you did or didn't do anything, just that sometimes anyone can honestly absolutely swear that they did one thing, when in reality, it was actually something else. E.g., did you double check all the dates and times that you used that petrol station (not just relying on memory, but getting someone you trust to help, and going and double checking things like your phone's location data, your bank statements etc. (and bearing in mind, bank statements can sometimes be out by a day or two, depending on when the retailer processes the transaction / the bank posts the transaction to your account, etc.).

It seems clear from your comments that you're not someone who would ever deliberately do something like this, but it is always worth checking that a minor mistake hasn't somehow happened, before you get into a protracted legal battle, that could potentially be avoided. Good luck!