Xbox – Bought currency for the wrong region – what are the options

Satellite connections are not recommended for gaming due to their terrible upload speeds (often a full second of consistent delay) even when there aren't any clouds in the sky. You'd be better off using your connection to try to score some desirable DLCs or small arcade games to take advantage of the higher download rates, although not if it takes a minute to load a webpage. In that case, your issues are probably coming down to everybody on your rig trying to use the same connection at the same time (assuming you are not in stormy weather). Try to find non-standard times, since your service provider may be throttling your connection during peak hours due to volume or as part of the contract. In addition, some satellite providers throttle your connection if your usage goes too high for the month. Don't waste your packets by connecting to the internet during storms at it will count against your usage.

If your issue is related to some network settings on the rig itself, that's something that you'd have to take up with your network administrator.

Supposedly prepaid Gold cards are region-free, although Microsoft controls this and their stance is:

Some prepaid codes can be redeemed only in the country or region in which they were purchased.

... which is extraordinarily vague, likely on purpose.

You might want to contact Xbox Live customer support before spending any money - it's generally very hard to get your money back from these prepaid cards. Also, counterfeits and completely fake codes are extremely common from less reputable sellers, so beware any crazy deals or promises from vendors.