Did u heared about "Imran's Broadband Helper Utility", according to its author

your service provider can implement a program on server side which can reveal that wheather you are opening some web pages at some fixed duration or not, and if not they often throttle your bandwidth or simply disconnect your connection (downloading a big file using utorrten of fdm is not opening web pages).
this sowtware can help you to solve this problem also, you just need to enable connectivity service under Connectivity Tab and assign some urls to open when you are sleeping.

u shoud try this.