This has nothing to do with sony. You'd have to go back to individual retailer and dispute it. If you ripped off the whole thing it's impossibro.
Edit: OOOH! So sony does do that
Welcome to the PlayStation Community.
Please ignore above response, it is not helpful!
Hello sony, yesterday I bought a ps plus one year membership but when I got to my house my brother wasn't careful enough when he scratched it and It and he peeled off the numbers so there was no way of identifying what the numbers were. Is there a way to get my money back or to get another ps plus one year membership card? Thank you very much.
Please contact (call) Sony customer support & if you're able to tell them what parts of the code you do have, they'll also ask for some other information, & if you can provide enough Sony should be able to tell that the code hasn't been used & provide you with the rest of the missing parts.
Here's Sony's number
11/29 - 12/1, 5:00AM - 12:00AM Pacific
Average Wait Time: Over 30 Minutes