Why does my credit card keep declining?

I need help, and I don’t know where else to turn. I have been trying to enter my credit card information to buy credits, but it keeps getting declined. My credit card company said everything is fine, and they don’t even see any attempted transactions for the credits. I have tried using Edge, Chrome, and two cell phones, but nothing works. Can anyone please help me figure out what I can do or why this is happening? Thank you.