How about a little math?

Let's assume you are sending 2 chat messages every second, and you are using your chat program 24 hours a day. (I'm over-estimating here ) Let's also assume that each chat message you send is on average 200 letters long. That makes about 988 MB of bandwidth per month...less than 1 GB. You said that you also like to visit this forum. Each page on this forum is around 20 KB average. Let's say you visit 500 pages on this forum every day. (I'm over estimating again ) That comes out to about 3 GB per month.

If you add the amount for your chat program and for this forum:
1 GB + 3 GB = 4 GB total for the month.

Therefore, there is no way you are using 40 GB of bandwidth with your chat program and browsing this forum...

On the other hand, let's assume your brother is downloading on limeware only 4 hours a day. (I'm under-estimating here...just to prove a point). Let's also assume he is getting slow download speeds of about 50 KB per second. That comes out to a grand total of 20.6 GB of bandwidth per month! And I would assume that he is downloading a lot more than that.

And there you have it.