Harassment For Reliance

sir, my self Sandip Upadhyay from kolkata......i am a good customer of reliance postpaid but I want to change my connection in prepaid so I talk custom care then he say pay your bill.. but again next month bill create my number so again call, A lady executives pick up the phone and say plz pay bill then am say First you change my number to prepaid then am submit your Bill..... Sir, then my outgoing, incoming call closed and my number is 9874415309 is use any other people.... again I call and ask how you do this is my official number .he say sorry but plz pay bill otherwise company take a legal action for you..... Sir, 1400 is not a big amount but this is wrong with me.... plz tell me what am do can I submit bill....