Ebay Ebay wont let buyers add complaints or change feedback on sellers after 90 days. Internet

I purchesed a amplifier for my daughters car on ebay 8 months ago. the seller has it listed as having a 3 year warrenty. I just ripped out my daughters stereo and installed new amps. the one I am complaining about did not work. seller would not resopond to my messages through ebay so i had to call ebay and they sent a courtisey message to the seller. the seller asked me to message her when I mailed the amp back and I did with tracking information. once again no response from seller. the amplifier was delivered back to the seller 6 days ago and I have recieved no messages from her so once again I had to call ebay. They will send her a courtisy message again.

 I also purchesed a Iphone battery from a differant seller 5 monts ago. It was listed as having a 2 year warrenty. The battery swlled up and poped the screen out of the frame and guess what? Another Ebay sell that wont respond to my messages.

Ebay wont punish these sellers or allow me to change my feedback because to much time has passed. There is no way on Ebay for me to warn other shoppers of these bad sellers. The Ebay lady that I talked to today said that is what feedback is for. How does that work when u cant change it 6-12 month out?