Unfortunately, there is nothing you can do than wait for a decision. The first thing I would have suggested you do was to call the embassy which you have already done. The visa process usually takes three months, but it can take more than that for one reason or the other.
Another option you can take is to ask your school to contact the immigration office in your university town to inquire about the status of your visa. However, this will have very little effect in accelerating the visa process since they hardly give priority to any one application.
I understand that awaiting a visa decision can be nerve-wracking, but I will advise you just to relax and wait for the decision. If you haven't heard anything by the end of August, try to contact the embassy again. Also, ask your university if it is possible to extend your enrollment deadline. All the best.