So I first I had a dual switch that stopped working a while back. The old switch was different than the new one, I honestly can't remember now the difference. However, when I wired it the fan would run constantly so I disconnected the fan plug. I finally realized I had put one of the hots on the wrong side. Never checked to see if fan worked right now as I already took the old one down. Fast forward to today and with a black going to the blue in the new light and black going to black for the fan with all whites tied together, I only get either the fan working or just the light when I switch them. No idea what I'm doing wrong. It did originally work right when I bought the house. Any help would be great, thanks in advance. Here's some pics.
Without all details or photos, you need 2 wire on each side of your switch or a single wire with jumper on your line in side, then 2 (2 black or 1 black and 1 red) wires from the load side. Whites all together. At your fan, you need white and ground and the 2 other wires. From load, 1 wire goes to fan black/blue/red whatever color, and the other load side goes to the light. Here, tie all whites together too. Here is a sample drawing I found: