Can i file a lawsuit if i was misinformed by my job i took a fmla because my son had open heart surgery i was told i would get paid while on leave but

The FMLA itself does not require paid leave and often, a person on FMLA is on unpaid leave.  But employers often have a pre-written policy as to whether your FMLA time off will be unpaid, or if you also take paid sick leave for part of that time.  Assuming that you would have taken the time off for your son even if they told you would get paid, it might be hard to take any legal action on this. Nevertheless, you should meet with an attorney to review the company's policies on paid leaves, FMLA, and use of sick time.