It does seem low but it all depends on how you drive it like all cars. The Megan e is basically the exactly the same underneath as my Nissan Ariya and would expect 205/207 miles per full charge in cold weather, which is what I got this morning at 0 degrees after a full charge.
I’ve only heard of one case of total charge loss with a Ariya, which was a problem with the normal 12volt system.
Good luck with it, I’m sure the RAC will find the problem.