The official website r4ids.net has announced that R4i Gold 3DS supports directly the newest 3DS V8.0.0-18 without any patch updating...
And the "MultiROM" feature demo for the firmware V4.0b2 is releasing...
Note: the firmware V4.0b2 is still in testing, it will be released within 2 weeks...
If it still can not work on your DS, you could try to contact with the sales where you bought from.
they should be responsible for the quality of their cards.
you could ask them for refunding or exchange one for you.