Since they already received the item they wouldn't be able to say the warranty ran out. Unfortunately certain parts may not be on the shelves at repair centers so they have to wait for parts to be shipped from somewhere else before they can do the repair. Another possibility is they may go ahead and replace it with a refurbished monitor but don't have one on hand.
At this point you are at the mercy of the supply chain gods. There may not be anything the repair center can do to speed this up. Replacement with a new one is only an option after the same device has been in multiple times and deemed a lemon. But if the repair center becomes unresponsive we do have a Service Inquiries sub-forum here. If you read the sticky it will give you the info you need to get someone to follow up for you.
A bus station is where a bus stops. A train station is where a train stops. On my desk, I have a work station…