VAT on Import from Germany with an EORI and GB Vat registered

I purchased some goods as a UK consumer from Germany where I was charged GB VAT at the point of purchase. The Germain retailer is UK registered, has a valid EORI and a UK registered GB VAT number that allows them to charge UK VAT at the point of sale and send goods to the UK, thus avoiding double VAT charges. However, my recent order was held by HMRC despite the documentation clearly showing all the above information on the commercial invoice and the CN23 (both of which had a signed declaration). How do I now go about reclaiming the overcharged VAT? The process seems unclear for an individual consumer rather than a business.

Hi,
You will need to speak with our Customs Helpline 0300 322 9434.
Thank you.

The problem with this response is that when you call this number and press the correct options to direct your call, the automated voice directs you to a ,gov website. It's this website that is unclear, hence why I asked the question here!

If the goods has a CN23 then that means they came via the postal service. It’s the Post Office or Parcel Force that will have missed the information that VAT has already been charged and charged it again. You need to lodge a claim with the Post office using a form BOR 286. https://www.gov.uk/government/publications/vat-customs-dutyimport-vat-relating-to-imports-by-post-bor286