Possible unfair dismissal after 15 years, need advice

Ive been at Retail company "A" in England for 15 and a half years, spotless record, I'm in upper management and have been for 2 years.

On October 13th I was taken aside and accused of taking bribes off customers (I accepted a £20 tip of a customer for great customer service the week prior), my first investigation was that day, I was sent home (with pay) and was told to wait for a letter, A letter turned up and I had my second investigation meeting the following week and then a 3rd meeting over video call party HR company to ask me some questions and today I got an email saying I was dismissed without notice pay.

Its all happened so fast and im pretty shook up about it and I need some advice.

A few things to mention, I was told not to talk to anyone at work during these 3 weeks, Ive been in complete isolation, nobodies checked up on me and I've recently discovered that my employer processed my Leavers paperwork and deleted me off the system on the 13th october (same day of my first interview)

Ive contacted ACAS and they have recommeded I appeal to the descision but theres no way I can go back to working for someone like that... What do I do?