Sorry to hear about your health problems. That makes everything else so much harder.
I can see both sides to this issue.
From your point of view, the defect wasn't apparent for a long time, so you didn't know it needed to be returned until after the 90 days. You were temporarily disabled and unable to try it out, or possibly unable to take it back right away (and didn't expect it to be defective when it was brand new). You've been a loyal customer. They were rude.
From their point of view, they gave you 3 months to try it out, and bring it back if it was defective. That's a lot of time, and it's not their fault that you were sick/injured during that time. They are under no obligation to take it back at this point, even if you have been loyal.
Also, CT has begun making it harder to return things. Even people who follow all the rules are being refused (see other threads on this forum).
Can you get it fixed under a warranty from the manufacturer?
If you are truly stuck with this item, I do have an idea. It could be considered dishonest or unethical. But, if you feel strongly about the issue, it might be a way around this.
You could: 1) buy a second, new item now 2) go back to the store with the defective item, and ask for a refund using the new receipt.
You might not feel comfortable doing this. At some point, you may need to lie. You might even get stuck with a new one plus the old one. The new one might be defective, too. You may need to do all this at a different store, who weren't even involved in the original transaction. But, it's an option (until they tighten the rules more).