Really it’s far more likely that you have a leak somewhere rather than a reputable company short changed your gas fill - likely you’re paying far more in service fees (& rightly so, re equipment costs, insurance etc etc) than the cost of the actual gas
Pick up a decent leak detector solution (rather cheaper than your gas refill fees ... and I’ll never understand why CO2 users lack this pretty basic kit)
https://www.swagelok.com/en/product/Leak-Detectors-Lubricants-Sealants/Snoop-Liquid-Leak-Detector
Apologies for sounding harsh, just meant as common sense and a seemingly low cost option