People don't usually respond as you describe, certainly not with intent to mock or otherwise make fun of you. I haven't been able to find out what upset you but here are some thoughts on your problem. As I understand things ...
If you are buying in the Mac App store, you can only buy for Mac computer related purposes.
If you are buying in iTunes, you can only buy for iOS related items.
So it follows your gift card would be rejected if you are trying to spend it in the wrong area.
Visa debit cards, even prepaid ones, are not universally accepted. You need to check the means of payment in your own country to determine that.
This is as good a place as any to put your question, but had it related to the Mac App store, there is a special forum for that.
Regards, 71.