Vinted complaint: Unfair refund

To summarise, on the 24th December I had sent a package off to a customer for an item I had sold. This item was due to arrive by the 27th December and it hadn’t. I tried to raise this issue and Vinted told me I had to wait until the 12th January to be able to raise a complaint about this. Closer to the 12th January they then told me that I have to wait til the 17th January instead. After going back and forth for weeks they have finally admitted that my parcel is lost and told me I would be compensated the full amount of the transaction (£630), upon checking my account I had only (roughly) £430 compensated. When I complained saying this is £200 short they compensated another £63. When I further complained saying that they just told me they will compensate me the full price they declined and stated that their policy says up to £500 will be compensated. After weeks of inconvenience this is completely unfair and unjust from them and is practically daylight robbery. I want full recompense for my item and the inconvenience caused by Vinted