MTS / Sistema Shyam TeleServices [SSTL] — Refund of extra paid amount

Address:

New Delhi, Delhi, 110025

For my data card no [protected], in the month of march i had to pay 1321, but due to mistake i payed 13221 and since then im calling them and asking them to refund my 11900 and have made complains about it constantly but every time i call customer care, they say they have reverted it through net but i never recieved it and in return they dont give me any details. Then they asked me to email in the customer care, i keep emailing them, they say they will send it through cheques but again they dont give me any further details and now whenever i email them, they dont reply me and when again i called in the customer care, theyre telling me i never made any complain but i have all the complaint ids and all proofs of it.