my hair wont grow

What are your ends like?  If it is not growing because it is breaking off, more small trims may be necessary to help it grow (cutting off only small amounts, like 3-5mm.) because if it doesn't grow because it is breaking off, this will help keep the splits in check so it can gain more length.  Average hair should grow slightly more than 1cm. a month, so cutting off this tiny amount should be made up for in less than a month.

Another possiblity is that they are taking off too much when you have trims.  How often do you get it cut, and how much do they cut off?  If you get a cut every 6 months, and they cut off 3 inches (7.5cm),  they are just cutting off all your new growth.  If this is the case, ask them to cut a lot less.  At this length, 1cm. every 3 months would be plenty...possibly more of a trim than you even need, depending on what you do to your hair (perms, dyes or straightening).