You have the right to receive your new salary that you and your company both agreed which is showing on your new contract. Before you go to the Ministry of Labour, it is best to clarify this with your company. My question for you though is why only now you are raising this question, shouldn't you asked them the very first time you received your salary last april? Anyways, if they will give you the rest of your salary, just count the balance from april to present. Good luck.