No Credit For Coins Won

I am playing the Mix-N-Match Pogo Slots Challenge - Win 7000 coins from Free Spins in 4 weeks! I have been winning with Free Spins but get no credit for the coins. This is not the first time this game has screwed me on a challenge that promises coins on free spins. These games are not new, why do the bugs keep occurring?  Shouldn't the games that have been around a while work correctly?????????

RocksNoSalt