I have been with this hosting company and using their backup plan for 5 years and I never met this problem before, this just came out this last few months.
as far as I know, they counted the backup usage based on the max. backup space taken each day.
for ex: on date 15th is the highest space taken is 40gb.
then they can charge us for the backup exceed 4gb. (40gb - 36gb)
but lately it suddenly changed, and they started to count based on the total 1 month backup.
so they sum the backup usage from date 1st until 30th. and starting to charge us like crazy..
I have contacted the account manager for my dedicated servers.. but the account manager almost never reply my email (very2 bad bad support
)
they are very big and very well known hosting company in US.
guys.. what do you think the most common backup plan for dedicated server? is it counted from max space or from 1 month total?
ps. the hosting company not that hosting my sites that writed on my signature (just in case you're guessing 
), they are very great indeed 
.