need help.

I am graphic designer in X company in abu dhabi for 8 months. when I applied for the job, they offered me 3k aed, but I will start as a trainee with a 2k aed in a couple of weeks. but when they showed me the visa it stated there that I will be a machine operator and will start a 2k aeds. I gave them all my papers with authentication of embassy here and in my country, but they said that they dont have much time to fix my papers, so they just listed me as an operator. my problem is, they did not honor what they offered me. they just increased my salary by 2500 dirhams when I first brought up the topic. and that was only 3 months ago. now every time I ask about it, my boss is just talking in circles blah blah I will be informed when he talked to the ceo or if I finished the 2 year contract I will get an increased then he will leave. and the worst part is I am the only designer for four branches in dubai and abu dhabi, and designer and operator in abu dhabi branch. And another worst part is the delayed salary which could take upto two weeks. I have been working very hard 6 times a weej. there are times that I have to work straight 9 hrs or more without taking a break. and they dont pay overtime. please help me. what should I do. what legal advise can you give me.