Hmmm. Don't know why they would stop you if all was by the book and genuine. Ours certainly was. I suppose any country could refuse anyone entry for any reason real or imagined, Schengen and Britain included.
I got one Visa for England in 2024 and one for 2025 both for my wife. The company who did this was Easy Visa in Pattaya and the agent is Paul King. Asto what you need to make it work I don't know and you'd have to ask Mr. King. Best of luck.