Op given you’re a photographer, have you had a chance to compare the exit data on your photos and the ones on the portfolio - especially if more have been added to the portfolio since you had your photos taken? I know it’s not conclusive but if you can show that the portfolio pix were taken with a high end camera and yours weren’t, or were taken with a different camera, then that would be suspicious. Not perfect evidence I know, as photographers do upgrade their kit, but they rarely go backwards and they usually keep a decent camera as a spare. But if they took rubbish pix of you and nicer pix afterwards, it would be useful evidence to add to your claim that it was a different photographer or one who was not using the high end kit you had a reasonable expectation of them using given the portfolio.
Have you reverse image searched any of the images in the portfolio to see if they turn up elsewhere? Or indeed any of your pix to see if anyone else is claiming credit?
Have you googled to find a pic of your photographer to see if you can check it was the right person? Or if anyone has a pic of your photographer (small chance) then checked to see if it comes up as the name you’re expecting?
Also have you googled the photographer/hotel/venue/wedding company/town/beach etc along with words like problems or issues or bad photos or law suits (might take a few attempts to hit on the right combination that brings back the results you need) to see if anyone else has had any problems?
Does the photographer have any Facebook or instagram pages you can use to see if it was him, if all his pix are bad but were good, what he was doing on the date of your wedding...
If you could find evidence he was taking pix at a different wedding for example (google his name and date?) - then that would be a massive help in proving that it wasn’t him that took your photos and thus they should refund you everything plus compensate you.
Do you have legal insurance with your house insurance/bank account/union/job that would be able to give you legal advice that you wouldn’t need to pay for?
Any way you could get others (people on a wedding website already thinking of booking in Mexico?) to make enquiries to see if they will double book photographers if somebody has one booked and someone else enquires about availability to see what they say? Even just asking if anyone has xx photographer booked next year or if booking at yyy venue/using zzz company next year, what dates and photographer have they booked as you’re concerned that you didn’t get the one you booked - I bet you’d get some responses and might get lucky...
Good luck - I know what a disappointment it is to get a bad set of photos back when you’ve got high expectations having seen a great portfolio.