No point calling Customer Services , all they will tell you is if tracking proved delivery, then you cannot claim any refund from eBay, as it then looks as if it may have been stolen? Was it left in an unsafe place? That is, one visible to passers by? If so items can, and do get stolen.
Has the seller provided you with tracking if not ask them for this, check the courier's / RM website and if it does not show delivery then you can open a case for item not received.
If you need help opening a case if there is no tracking showing delivery, from what you say ' claimed it was delivered' kinda suggests tracking has shown delivery, but if not, come back to us here.
@mktdra12