Road accident case

Recently we hit a scooter with our car. No one is injured. The person is driving the scooty and his mother is sitting behind. She fell down after the scooty stopped after 10 to 30 seconds. She had no injury but still we took her to the hospital. The doctor was their relative. She was admitted in the hospital. She was in shock. They took xray, ctscan and everything is fine in the reports. The person did not file an FIR but called their uncle who is working as ACP. He took our car paper s and driving licence Xerox and after 3 hrs told us to leave. After 3days the person called us and asked us to pay amount. We accepted to pay because it was only 4000 at the time we left. But we don't know what more test d they have done they asked for 20,000 rupees. They are threatening us that they will file FIR with the evidences of cc footage and doctor report as the doctor is their relative it will be in their favour. The lady had no single scratch on her body. And also they have the help of ACP who is in the police department and he can help them. Please suggest us what to do. We can't pay that lumpsum amount