That's a common problem with air rifles due to the constant play between the rifle and barrel. ( if it's a breaking pump ) If two different scopes are doing the same, I would say it's the barrel being misaligned with the rifle. Swap it for another rifle. My crossman 880 does the same, but it's is only inconsistent high and low.
Ok, I went back and checked some reviews on your gun. Even though it's a "fixed" barrel, which is a good thing, it is known for poor sighting with a scope due to the way it mounts and lots of plastic parts on the gun leading up to it. May want to stick with the iron sights? Have you tried pellets? It shows much better accuracy with them. Cool looking gun though, just a lower end grade. Have fun!