That's very interesting that the contactless 'was down' and the CCTV 'isn't working' and yet there's no possible chance that something else might have gone wrong to charge you £65 for one pizza, so it must have been your mistake....
This is obviously a regular scam that he pulls - probably seeks out victims after the pubs have closed and who don't look like they might threaten or deck him (CCTV is broken, isn't it, so they'd get away with it, wouldn't they....?)
Aren't most card payment machines these days linked to the till, so the amount displays automatically? It's a long time since I've seen somebody have to manually type in the amount payable by card, except maybe for a market stall or mobile food van.
As well as all of the excellent advice about raising a chargeback, definitely spread the word on SM. There are probably others who will come forward, who thought they were alone and that nobody would believe them.
If you find a few other victims, you could even approach your local paper and give them the story about the problems with faulty card payment technology, which has beset you all, and criticise the lack of support given to the pizza shop owner by their card processing company, as the system seems very difficult to reconcile - pointing out that customers will be concerned about going there. There will quickly be a flurry of comments (from customers and other business owners) to the effect that "Well, MY (local) shop never has these problems" and "If there is a keying error, it's very simple to correct it".
Without outright accusing them of anything, the message will come across that (for whatever reason) using this shop proves a real financial risk - always in favour of the establishment - and then, well, it's up to people whether they want to go there instead of businesses that don't have the same 'problem', isn't it.
Even if he came clean (or more likely claimed that he'd finally forced the company to fix the 'glitch'), the loss of trade and goodwill in the meantime would be way more than the extra that he scammed.
This is exactly the sort of behaviour that leads to massive 'Business Under New Management' banners covering the whole window appearing before long. When genuine, honest, respectable business owners sell up because they're retiring or moving or whatever, the new owners invariably don't mention the new ownership/management status at all.