Guitar for beginner - advice needed

You likely have a capacitor in the tone circuit unsuited to that humbucker. Did you start with two single coils, and now it’s H in the neck and S in the bridge? If so, here’s a wiring diagram from Seymour Duncan for that; note the .47 cap in the tone circuit. ETA: actually, I bet you have the cap grounding the hot side of the pickup and ignoring the pot, which would bleed all your treble to ground. Recheck the connection at the pot against the diagram I linked to.

PS: you can test this theory by unsoldering the cap on one side – you should instantly get a ton of treble.

Yes, it was standard Tele set-up, and is now H in the neck, S in the bridge. I will try that suggestion, thanks.