You need to find the tracking number. If it was supplied by a post office which you visited go back there and see if they can access any data that can give you the number.
It is not a silly situation , and is your fault. Tracking numbers by their very name are there for a purpose. You are asking for help but you currently can't prove the kit was posted, it is only the word of a complete stranger. This is what BT would tell you. You could have sold the kit on an auction site for all we know.
Hopefully the post office can dig up the number, if they can't then you have a big problem.
