You should reach out to the Student study Centre. You can reach out to them at: ssc@ignou.ac.in . This is because IGNOU has its own rules for assignments and exams and the Administration takes final calls but there might be exceptions based on case to case basis. In general, you have to submit assignments for all subjects but pay fees for the subjects that you want to appear for the exam. But we would still suggest you to confirm the same from the Student Study Centre.