That is a likely a carbon spot that are usually caused by the copper/gold alloy in these coins. They develop over time and I've had them "pop-up" after I bought AGEs. Buying .999 gold like American Buffalos greatly reduced the chance of spotting because they are not alloyed. The spot has no effect on the value of the coin and I wouldn't worry about it but it's your coin. The $25 partial refund is what I would take.
ANA #R3154474




















