Squire VM Jazz Fretless Neck Adjustment..

I may be showing just how ignorant I am but I am really struggling to get the neck on my new acquired Squire Fretless adjusted correctly. I have never had to make this much adjustment on any guitar neck (bass or guitar). It's usually a couple turns and done. I have had this guitar for 3 days and each day I have had to adjust the neck 5-8 turns.. and in a couple of hours, it will be right back where it was prior to the adjustment.

Am I doing something wrong?

 

Gypsy, I don't think it is stripped because the neck is definitely moving when I adjust it. The problem is when it sits for several hours or overnight it looks as convex as it did before I made any adjustment. While adjusting it this afternoon, I guess it ran out of adjustment because I can't turn the truss rod nut anymore. Its going back tomorrow. I don't know if I'm going to try another one or not. I have a really nice Pbass Special (PJ) that I hardly play anymore since I picked up an Aerodyne, I may replace the neck on that on with a Warmoth fretless neck. It would be about the same amount of money out of pocket, but I'd have a much nicer bass with an active EQ.