We you able to redeem your promo code on piggericks.com and did they appear in your piggery? If so, everything worked as it should.
Pigs are (at least on Piggericks) not very loyal creatures so they may indeed defect to your enemy after you lost a battle. You can see what happened to your pigs if you go to the history in your menu.
If, however, you never even received your pigs, could you contact us on Discord or Telegram, so that we can take a look at your case in detail? :)