Sounds like your local delivery office are playing silly buggers, to say its out for delivery when its sat in the warehouse is disgusting.
Unfortunately not uncommon with Royal Mail.
I currently have a small "package in the system" from an Amazon third party supplier, ie, not dispatched by Amazon, can't fault the supplier, was dispatched to Royal Mail within an hour of the order being placed and Amazon supplied the Royal Mail 24hr delivery tracking reference number.
According to the tracking information, package arrived at my local DO early hours yesterday, Saturday and was shown as out for delivery by 3.00pm, nothing received.
This morning, Sunday Royal Mail tracking still showing the same information
I'am reluctant to order anything from Amazon that's not direct supply by them, had no choice with this particular item, have found that Amazon's logistics work and their tracking information is always accurate, never had any issues.
Yet Royal Mail still wonder why their business is struggling