Machine drilling too deep

Hi,

As I was using the CNC machine, it cut through my material (3mm) and the sacrificial layer. I had programmed it to cut with the depth of 3mm. The code the machine was reading showed that it was supposed to be cutting 1.4 mm while it was actually cutting about 68 mm deep. I had already calibrated the surface of the material to be 0 on Z axis and I even started the cut at a higher level of 30mm. How can I solve this issue, and what could be causing this problem? Is there a way too put a limit on the machine so it will automatically stop after a certain depth?

Thanks,
Ariana