Customs not paid by buyer

So I sold a couple of phones on eBay , normal enough . But the buyer sent me a photo of a customs charge 50 something pound (UK) I stated yes as UK is no longer in Europe , there was many delivery attempts but refused to pay the customs . The phones are now being returned to me . The funds on eBay have been available over a month . The phones were sold 2 months ago and only today the buyer raised an issue through eBay that the items were not received . What’s the legal view here ?