If it's £10 to £12 in Tesco, why not buy it in Tesco?
Buying from unknown sellers on eBay is always risky (and so is selling to unknown buyers!). eBay is a jungle.
It may be worth it for items that would be difficult to find anywhere else. But if you keep being let down by eBay sellers for something you could simply buy from the local shops, surely the answer is obvious?
If you have ordered an item almost a month ago and it hasn't arrived you need to use eBay's money back guarantee before the 30 day time limit runs out, see: https://pages.ebay.co.uk/ebay-money-back-guarantee/