Vodafone India — postpaid to prepaid not done even after 2 months but postpaid bill keep coming

Address:

625001

I have been chasing vodafone customer care to change my number 763xxxxxx3 from the month of august.
The postpaid service to the number is disconnected in august month itself.
But prepaid service has not yet been activated.
I have been keep calling customer care, every time they give one reference number and telling the service will be activated in 1 day but till now my prepaid service is not activated.
They also asked me to visit the vodafone store and submit my documents but whenever we submit the documents they give new prepaid sim and asking me to pay the bill for postpaid service every month.
Please note that i have made the request to convert my number to prepaid in august month itself and i have unnecessarily paid the september month bill without any service from vodafone.
Now october month bill also came. I will not pay this amount as vodafone has not changed my service to prepaid since august but keep sending the bill for every month.
I am totally frustrated with the service provided by customer care and the madurai north veli vodafone store.
Can you please look into this matter to remove these bills and activate my prepaid number?