Firestick Lite Dull & Pixelated picture help please

[PallPat]

Guy's I've bought a Firestick Lite on October last year. That Firestick is fabulous with amazing picture quality superb sound. I'm more than happy with my purchase. But all of a sudden from last few weeks I'm facing issue with 5Ghz Wi-Fi band but 2.4Ghz working absolutely fine. Then on 10th January I called Amazon and their support executive make a replacement request for me said only return the dongle not the accessories (Adapter, remote, cable) and within 5 days I got my replacement Firestick with all accessories but the box looks like old and the company seal is broken and in the box it's written "Warranty Not For Sale". Then I plugged my Firestick to the same HDMI port but picture quality looks dull(low brightness) and YouTube 1080p don't look as sharp as previous one. And when I play any video with grass (like football match) the grass looks blurry with jagged edges which we call anti-aliasing in gaming. Now I'm extremely desatisfied with my replacement now what to do?