You open a case for breach of contract at the local Court. You’ve paid, a contract is made. If they’d just promised, or if you hadn’t yet paid it would be different
Take a look at this from same seller
https://www.ebay.co.uk/itm/Steel-Pickup-Cover-Protector-for-Jazz-Bass-Electric-Bass-Guitar-Replacement-V9F2-/133978486786?mkcid=16&mkevt=1&_trksid=p2349624.m2548.l6249&mkrid=710-127635-2958-0
I don’t think anyone is insulting your use of English and as I’ve said before I hadn’t realised you were not a Brit until quite recently. Sometimes “lost in translation” can be a little more ephemeral than strictly use of language and encompass other things