I think what is being shown, is in fact 1 day extra than what u r supposed to get. Rs.400 Cashback + Rs.441 of free Platinum HD pack = Rs.841 in all.Now, the month of September has 30 days. So 441/30 = 14.7 per day. And at this rate, at the end of 30 days, ur balance will remain at 400 Rs.To be on a safer side, more favorable for u, lets assume from now, they will deduct at 441/31 = 14.22 per day (Being October). That comes to about 28 days.So, in all u r eligible for 58 days of viewing.Now calculate that from ur installation date.......starting on 10th September:21 days of September+31 days of October means 52 days are gone. So now.......u shud have been eligible for only 6 days of November as against which, they are giving u that fraction of a day as full day, extending ur expiry period upto 7th.