Mts — Regarding MTS DATA card postpaid Connection

I am from trivandrum, kerala. My MTS DATA card # [protected]. On 3rd Feb2015, I requested to change my Post paid connection to Prepaid connection and paid all my dues with prepaid amount (Rs549) and gave all related documents to but the showroom people ( Ciya Communication Kp 4-80C, Vadakkumbhagam, Near Kazhakoottam Police Station.Pincode : 695082., Ph #[protected]) did not pay my money for my connection and the connection was still active. so i went again on feb20, 2015 and i ask them to check my account, the amount is not paid and on th same day they did the payment. my connection got disconnected and not changed to prepaid. again last of feb2015 i went their they said with in 7 days the connection will be active. again they ask me to submit the documents i gave the documents. last week went to enquire about the status they said we cant do the connection to prepaid. so i request them to give me as post paid connection but they ask me to buy a new device Cost around 1200Rs already my device same cost. now i am losing my device. Please do the need full to change my plan to prepaid. Still now my device is useless