Upvote:1
I don't see what the problem is. 9,135 is indeed between 8,500 and 9,500. I don't know where you got the oh-so-exact figure of 9,135, but it sounds like a statistical average. And lo and behold, this average in indeed within the range given to you in the offer letter, which was probably written by a human being, who was aware that people lifestyles and need influence how much living expenses are required – hence the low and high figures.
Upvote:1
£1,015 per month (£1,265 if studying in London) is the required amount of funds for a Tier 4 visa (see here, p. 45). Evidence of living costs you have to provide is capped at 9 months, so that if you plan to stay for 9 months or more, you need the evidence for £9,135. I advise you secure at least that amount, unless your offer letter provides an official source for the lower amount is cites.