fraud Institute asking for money without giving proper knowledge

i had been to an institute for a course i paid registration amount but when after few day i realize that the class was not giving the proper knowledge and they are continuously asking for payment and threatening that if we left their institute they will give us the legal notice, so is there any procedure that we can take them to some legal notice or so that will help the students? they have also not given the slip of advance payment stating that they may cost them 2%.