Need advice regarding I-539 application,case is taking longer than the processing time

I have applied the change of status application (I-539) from H4 to F1 in the month of Dec/2014 and I have got a receipt no on Dec18/2014, till now my status was not changed. In the meanwhile I have raised numerous service requests and i spoke to USCIS officers, but no luck.Could any one please suggest me how i would like to proceed.