You do NOT want a replacement.
There is no reason to believe any replacement (if it even arrives) will be any better than the original.
Go to the Resolution Centre at the bottom of this page.
Open a Not As Described Dispute.
The seller will be required to send you return shipping.
If he does not, he is required to refund.
If he does, ship the item back, and when it shows delivered, he is required to refund.
If he does not, eBay will, and go after him for their money.
The first suggestion in a Dispute is to contact the seller, but that is just a suggestion not a command, and you have already done that.
Open the Dispute, ask eBay to step in and escalate to a Claim as soon as possible.
By the way.
Most warranties come from manufacturers, and most manufacturers will not honour warranties from online sellers (with the exception of accredited retailers) or from resellers.
A B&M shop may have their own warranty backed by their own staff, again not usual with online sellers.
You do NOT want a replacement. You want your money back.