Poor service

I've been buying hardware from Mica Boskruin since they opened. I generally have a good relationship with guys that work there but recently, when I topped up my gas cylinders, I noted that they charge for more KGs than the difference when I weigh the cylinder before and after filling. Like today, they said they filled 3kg but the difference in weight was only 1.5kg. Despite my long patronage, they treated me with disregard. I'm very disappointed.