Jolly good letter Flopps.
You were given the most appalling run-around - and to then be charged for the privilege of eventually receiving your parcel, is an absolute disgrace!
Some years ago, we too, had cause to write a letter of complaint to Royal Mail. It concerned something which had gone astray (at that time, we had a very dodgy postman, who turned "losing mail" into an art form...) But the real insult was the (unwanted) "recompense" sent to us by RM. A small, tin post-box containing some boiled sweets!
Hope you receive a decent apology and get your money back.