Usually, it is extremely rare that FPSC will overturn a rejection. As far as i know, I haven't heard of such a case. It depends on the reason of rejection cited. If you feel like you did not commit any errors in your application procedure, then your best shot is to call the FPSC headquarters (number is available on the website) and get in touch with someone and explain to them. Only then will you know what to do next. Generally, they are quite strict with these matters and do not overturn rejections. Best of Luck.