Brand registry problem

hi all

i have a brand which i have been selling the product on for a while now, i have other people on my listing who are also selling the product. it is a generic product but it shows my brand name in amazon.

someone has registered my brand name as a trademark in the UK and have applied to amazon brand registry with the brand name and are now trying to kick me off this listing saying i do not have authority to sell this product

can anyone help in what to do in this situation, or if anyone had this same issue what did you end up doing

thanks in advance