Glitchinthesystem

I have been using a Japanese proxy service company (sender) to purchase used items from Japanese websites for the last two years. When I request my items to be packed and sent to me, I always ensure that the value is below the £135 threshold, and the Japanese company declares the items as "other", given the nature of the purchased items, and lists individually all items and their cost. I have suddenly been charged 20% import vat on four packages I received via FedEx, because the sender incorrectly declared my items as "gifts". I contacted the Japanese proxy service company and they admitted it was a "glitch" on their system and that they should not have been declared as "gifts", but they said they cannot do anything. The items were clearly paid for as their individual value is stated in the declaration form and the sender is clearly a company on the paperwork - so they are obviously not free "gifts" sent from one private individual to another. All packages are below the £135 threshold but obviously above £39 in value. I contacted FedEx to say that there is a mistake in the declaration form and they should not have been marked as "gifts". Is it possible to amend or dispute the VAT import charges, when this is clearly a mistake by the sender on the declaration form?