First, there is nothing wrong with your scope.... (and it would help if you told us what rifle and caliber, what scope mounts, etc).
Shooting past 1,000 yds is more than just slapping on a scope and blasting away.
Mounting the long range scope
is both an art and a science, and it takes planing.
Having the scope's elevation at the top of it's range is the worst place for it to be.
The erector cell bumps into the top of the scope, and tends to float loose, because at that point, the erector cell may not be touching one, or both, of the spindle faces. In effect, it is on it's own, wandering around after the recoil of each shot.
As Martha Stewart would say, "... and that's a very bad thing!"
All of my rifles (except two tactical match rifles), have the scopes set up so the 100 yd zero is just a few clicks off the bottom of the elevation.
This accomplishes two things... first, I get all the elevation I paid for, and with modern, flat shooting magnums, I can get way past 1,200 yds with plenty of elevation to spare.
Second, I never loose track of the elevation, cuz "zero" is at the bottom of the range... so if 900 yds is 26.75 moa up, I can almost dial it in the dark.
My 50BMG rifle is set up so from the 100 zero, I have 147 moa of up, and 2 moa of down.