Hello !!

I was wondering if someone could help me with a postage question. I got 2 of my Holiday cards because of insufficient postage. Both are ISAIS addresses. I weighed each one, and put the appropriate stamps, actually with extra with 2 forever stamps. My understanding that one forever stamp covers up to one ounce, which is 28.35 grams, and mine was about 45 grams, but I used 2 forever stamps. So I don’t understand how that was insufficient stamps. The other awesome people I sent it to received it, and all of them were the same weight. I just don’t know why... does anyone know why ?

Edit : OMG I was talking while typing, instead of USA I basically wrote ISIS !! I’m definitely not sending Holiday cards to ISIS !!! 😳

P.S.S it’s a flat envelope that fits the mailing standards