PATHETHIC CUSTOMER CARE!

Purchased a Dynamic Posture Pocket Bed for my back pain. However within a few months, bed is already sunken in the middle - giving me worse back problems. I then contact the bed shop as i know my bed is under 10 year warranty, and asked what my options are cause surely the bed cannot be doing this. I am then asked if i have my original invoice, I looked for it, cannot find it but i do have my proof of payment. i then tried to go to the store where i purchased from, only to find that the branch has closed down. i am now told that they are not able to assist me without this! i find this totally ridiculous as since covid, most things are kept digitally. HOW CAN THIS PURCHASE NOT BE ON THEIR SYSTEM? WHY CAN THEY NOT GO THE EXTRA MILE TO HELP ME AS I HAVE PAID A GOOD AMOUNT OF MONEY FOR MY BED!!