I wouldn't worry about food safe if i'm being honest.
I would bet my next brew on it, that the only difference is one jumped through hoops to obtain a certificate, another one didnt.
A shame you don't live near me, I've a couple of toothpaste sized tubes going spare.
As for accepting a partial refund, if it did come from CN, had you gone back to the seller and rejected his partial offer, he would have given you the full amount back.
The cost of shipping it back, far out weighs any profit he may have had in it.
By offering you a partial refund, he's broken even, and you're probably out of pocket having to fix it.
Especially if it came from Ebay.
I see so many sellers advertisng as UK Stock and it comes from the far east.