They’ve got stolen property, innit mmm… I’m not sure the police are going to want to get involved in that one! I’d take some convincing that it is ‘stolen property’* if they took it in and then simply didn’t answer the door. I imagine you will have a problem getting the telephone operator to consider this warrants police involvement. If you can show you have tried on several (at least three occasions) to get the goods, and that each time there was an adult in the house who refused to hand over the goods or answer the door then it might be worth asking them for advice.
(* in Scotland this may be Reset, but only if there is intent which is hard to show from someone not answering the door once – perhaps one of the people was standing bollock naked behind the door at the time. I don’t believe the equivalent exists in england – and Handling Stolen Goods requires them to have been the subject of theft).
The company who supplied it will not be that bothered as they have a signature, and your money – it will be your job to prove it didn’t reach you and you couldn’t get it from the neighbour. If you are ‘lucky’ they will pass it on to the courier company – who will, like all such companies be disinterested.
Good luck.