I believe Lee will suggest you contact the dealer; especially since they re-gassed it (supposedly) to correct a fault.
It would appear they failed, or took the cheap hopeful route to appease you.
Do you have any sales literature, advert, or anything that mentions the AC as functional, or not.
As a retail sale you are protected by various consumer laws.
If they are forgetful of this, maybe they just need a polite persuasive reminder before you contact Trading Standards.
I find Trust Pilot very useful for publishing (truthful) accounts of poor business practices and behaviours (although t5his seldom produces any 'progress'.
Any decent AC place will be able to re-gas it. The better ones will also have the equipment to locate a leak (using a special dyed gas).
However, a competent repair shop may be a little more difficult to locate, assuming one is needed.
Some Toyota dealers, but by no means many, will work on an imported Alphard; so it is worth checking around your locale for peace of mind.
Good Luck.