You will not pay VAT twice, as long as the sender / seller put the information on the bill of lading - i.e. British EORI code: GB 365 6085 76 informing customs in the UK that the tax has been paid. Otherwise, VAT may be charged again. Read page 16-17 carefully from the link I provided earlier. Ebay charges 20% VAT regardless of the actual VAT rate on all products with a value below £ 135. If the value of the product exceeds 135 pounds, Ebay will still charge 20% VAT but you can try to recover overpaid VAT using the BOR286 form -
https://www.gov.uk/government/publicati ... ost-bor286
You will almost certainly fail to recover VAT from Ebay or Allieexpress. Likewise, the request for a VAT refund from the seller is groundless - because the tax collected by eBay / PayPal does not go to the seller but to the account of the UK tax office.