Just been looking on CJS keys and they have Windows 10 pro oem key for £17.43... if it's all legit how can they sell it at that price?

I couldn't tell you mate, but smart money bets on how the company reacts when things go awry, not when they go to plan. All companies make mistakes, but some aren't all that interested in resolving issues after they've taken the money.

Given your experience I think I will give them a miss.

I'd used them before my issue and I've used them after, the fact that they refunded me my money gives me no reason to not want to use them, I'll agree they certainly aren't the most professional company you'll come across but I can only talk from experience and in general it's been good and if they save me money then I'll use them

Don't have these issues on consoles Only problem is they cost 4 times as much .

I don't know ? You bedroom Dwellers

Keys are bought from different countries, so through currency conversion they can sell the keys cheaper.