Like I said, you have used all your monthly data allowance... Upgrade to a larger plan or purchase tokens.
10GB divided by 30 days leaves you with 333~ MB worth of data for each day, which can easily be consumed as you have noted, especially if you do any form of streaming video such as youtube, or netflix.
As far as knowing why your data was taken away... ask your self, and family members?
I'm glad you received the new modem and were able to get it registered successfully. Just make sure you remember to return the older HT1000 modem using the return label provided with the box. As far as speeds go. We'll need some tests so we can see exactly what you are experiencing.
Please head over to www.testmy.net make sure to only use 12 MB as the test size, then run a set of 3-5 tests throughout the day and post your results. Since you have already used up your data allowance, I have added some token bandwidth to you account so that you can run these tests while not throttled. Depending on your results we can get our engineers involved to directly work on your site. We hope to hear from you soon.
10 was a joke to us too. I had to go to their highest and it's 25 and it doesn't last long with 3 kids. I wish they had more options. We had exede and hated them, they are a joke too. Unfortunately, I live out in the country so our choices is limited. Only 1 mile down the road everyone gets to go through a local company and they get unlimited for way less than Hughes charges for 25.