Diners lame explanations

I went to swipe my Diners card for my airline booking. Was declined. ! First time ever was my cards declined. Called Diners. Said it’s Saturday (morning) and that “new customer” dept is closed. But I said I’m a customer for over 10 yrs plus ‘. What was reason. We used cards for international booking recently no issue. Many years we used card Response was limit was reduced to such a min amount that cannot even buy single ticket. I was shocked. What is the reason. We have many other cards and all are paid up with good limits. We actually stopped increasing limits offers to us. Diners agent said that due to us being offers a new Credit card which I declined as my current card is sufficient they unilaterally dropped my limit over 80% !!! So I don’t want another card and extra Credit therefore my “affordability “ is now questioned. ??! I must wait till Monday But in interim my booking cancelled it wad totally embarrassing to have agency call to say that you been declined. Does this make any sense. How makes these decisions, what basis , where is the customer service , a person with excellent Credit history is downgraded as they don’t want to take extra credit ? Excuse was the country financial act is reason. What nonsense. If that’s case our business, finance , other cards erc would been impacted. Diners service should be realty looked into as recently too many issues arise and it’s very difficult as the agents cannot assist.