How the forget...
In 16 years, I have NEVER scratched a gift card so hard that the letters are removed. You need to seriously calm down or something when you scratch these codes off, mate.
^
I study printing pres stuff and I honestly doubt they will come off unless:
The scratchable foil thing is very low quality, thin printed or bad printed
The ink hasnt dried yet for some reason
You apply too much pressure.
And it's probably to last one because bad prints usually get thrown away and the ink is probably dried using heat or UV light wich let's them dry almost instantly (implying the card are plastic)
These cards are usually made in another company, try contacting them