My prepaid mobile 9757XXXXXX was being charged Rs. 5/- per every 5 days for some service which I never subscribed to. The message was coming from 520202005. Instructions to unsubscribe never work. Wrote multiple e-mails. It took sometime but the money got refunded. Glad that I did not have to discard this number and switch over to private network, otherwise I was considering. MTNL has the advantage of wide network coverage than any other operator and deductions for unnecessary reasons are less.