Did you record him admitting what he did?
Because if you didn't, he may very well deny it if the police contact him about it.
You could tell him that if he doesn't replace them by next week, you'll be reporting him to the police for criminal damage. You should start off by doing it in writing, do you have his number to text or WhatsApp him? You could say something like "Alan, after our discussion regarding you deliberately chopping my bay trees down that are by my front door, I expect replacements by the end of the week."
Don't threaten him, but if you've heard nothing by the end of the week, follow it up, with a "Alan, I'm disappointed that after you deliberately destroyed my bay trees that you have failed to replace them, you've left me with no option but to report you to the police for criminal damage."
That way, it's all logged in writing. But if he doesn't acknowledge it in writing, it's still not evidence that he did it.
He was ridiculous, you are allowed to trim hedges on your own side. Also, you need to check first that there aren't any nesting birds, to those saying you cannot trim them at this time of year, you can, as long as you've checked that there are no birds nesting in it. If there are, then you cannot.