ES1 doesnt care about Mac Address. Sify had not implemented it MAC policy then, so it seemed prudent to keep the executable as small as possible by removing mac detection routines. Sify doesnt authenticate against IP, only against mac address.
Which is not good. You are kinda of stealing other peoples accounts/time/money.So it amounts to hacking and abuse. I would ask you not to use other peoples accounts. Additionally please call sify and have your mac settings reset.