Thanks for posting. Apologies that you're having problems with warranty support.
Here is information from Dell-FAQ regarding monitors and how to register them for warranty support.
Hi Tried to call the service department - no help at all. they can't find any of my monitor's details and said they cannot help with out a receipt. I don't have a receipt.
Can't get a copy of the documentation no matter who I ask. The manufacture date clearly shows it is in warranty and it has all the tags, serial numbers, etc. The support desk state they cannot help me without the receipt.
We may be able to find something for you. Please send me the below information in a Private Message:
A picture of the rear label
U2715H Service Tag number
U2715H Express Service Code number
U2715H 20 digit S/N
Name of the seller. Link to the seller website.
Your City, State, Zip Code:
Did you try to contact the seller & check if they can provide you a duplicate bill? I am afraid, there is nothing much that can be done if there is no proof of purchase. Since the service tag does not show up any details, the concerned team will need to validate the purchase & then associate a warranty to this system tag which cannot be done without a valid invoice copy.
For my reference, please click on the message tab next to your avatar– click “New Message” & search for my Dell username (Dell-Sreejith R) & send a private message with the service tag, registered name & email address.