Problem in Site Collection Quota

I have created the site collection with site quota of 70 GB. And i Kept Warning alert message when the Current Storage reaches to  60 GB. But i am getting the warning alert message as below when the Current Storage is reached 48 GB only.I cant able to upload the documents to the site collection.

Steps taken:

We have checked with adminrecylebin(http:"Site Collection URL"/_layouts/adminRecycleBin.aspx) in the particular site collection, we have found lot of files there with 100 MB size each, is this causing the problem? if not then what will be the possible root cause?