I can clean a cat converter too with super hot water and some mild organic acid to brighten the substrate only if mildly poisoned, I can also accomplish this by accelerating the car vigorously at highway speed for a solid 20 minutes to self clean it.
But if the cat is plugged with solid debris its dead, I throw it out and replace with new part
That motorclean workshop outfit is literally garbage, i can bet you they will never show you any pressure test of a cat before their job. I still have my open offer for them to clean DPF of diesels of heavy haulers by few hundred count every week. They havent replied yet and their provided addresses are all fake too.