Hmm, that is pretty awful. I remember I changed our quote with Pickfords about four times, and they were polite every time (that must have taken some effort

).
Also, I can recommend asking the mover to come by once you have packed or are close to knowing what you will take. Most should do this free, and they will indicate how much m3 you will have. Should take about 10 minutes.
We estimated ourselves and had no none come and visit, and although the estimate was right, I would certainly have someone come over the next time, as they will also explain how they want things to be ready. This saves you a lot of hassle and stress on the moving day.
Also, if you overestimate, or underestimate, your final price will be much higher (or you are paying too much), because they will reserve part of a container, and if you suddenly go over on packing day, you might need a whole new one....