If it were me, I would ask why the dive was cut short. I was taught to manage a dive plan to get at least 50mins. However, sometimes dives are cut short due to vis, weather, or other diver problems. I was at Hin Daeng and we had a big air hog, who even with a 15 liter tank hit 50 bar in 20minutes. Not saying any of these things happened on your dive. There could be a reasonable explanation or they could be lazy, but the only way to find out is to politely ask.