Post paid to prepaid conversion

I had visited vodafone stores on 18th of Nov 2018 for conversion of my postpaid connection to pre paid. I had completed all the formalities and had also paid in advanced un billed as well as billed amount. I have also paid extra amount in advance for the prepaid recharge. I tried to contact the stores again several times after that incidence for taking the follow up as the card didnot get converted to prepaid. The store had once received my call, took all my details and told me that they will get in touch with me immediately. But there was no response form the stores. Even after repetitive calling the stores, they were not answering my call. Then after at least 10 times i have raised a request t the customer care explaining the situation, still the query remains unresolved. I had raised complaint to the nodal officer as well, still the query was not resolved. Today on 23rd of Jan, when i had visited the stores in person, they are claiming that i have used the connection, so i have to pay the bill for the same, only then the post paid connection can be converted to prepaid. Kindly suggest me a solution, as i have received very unsatisfactory treatment from the vodafone stores executive saying that it was my mistake. According to them, i should i have visited the stores again. I have every hard copy of the transaction i made with vodafone for the post paid to prepaid conversion. I wish to take this issue to the consumer court. Please guide me. Kindly let me know if i am at fault.