If the scope is not holding zero, you may have found out why the rifle was for sale. The previous owner has given up too soon.
Invest in a scope that'll hold up to the unique recoil a hard kicking springer air rifle delivers and you'll be fine.
My preference is a Hawke Airmax 4-12 x 40. Doug at Cameraland has sold 3 to me. Of course there's others that work well too.
A solid rifle, a solid optic properly mounted and a quality pellet (heavy for caliber).
Let us know what you figure out!