Does not hold zero! - Pulsar Trail XP50 1.6-12.8x42mm Thermal Imaging Rifle Scope

I am very disappointed with this scope. I can't understand why it won't hold zero?! I take out to the range and sight it in just fine, nice groups and all but then I go on a hunt next weekend I can't hit a darn thing! Pulsar customer support only gives me excuses and tells me I am not zeroing the scope correctly... This is not my first thermal or digital sight, checked and rechecked mount, setting etc.... How do they explain the other bad reviews about this scope not holding zero?