Maybe it's because your idea of a special gift is not theirs, even if sent with the best intentions.
I'm guessing in a lot of aid countries a geometry set, pencils and paper and seeds and trowels would go down rather well, not a teddy bear and a tin of spam, which with the best will in the world, is what these boxes usually contain.
You can stop charities spamming you by texting back with whatever the word is, usually stop and if you ask them to remove you from their lists they will.