International payments declined using Mastercard from Standard Bank

I have had a Standard Bank MasterCard for many years, and use it for all my online shopping. On the 3rd July 2024, my payments started being declined. These are all international payments (Amazon / Kindle / Paypal). I cannot now make any purchases from these vendors using my credit card. I have contacted Standard Bank 3 times, and have the following answers to why my payment was being declined: 1. IT problem - with no idea of when it will be resolved 2. Mastercard have imposed some compliance rule which insists that the cvc on the back of the card is supp****. Unfortunately, I cannot provide the cvc when I enter my card information at the vendor. Is anyone else having this issue? Is it a real Mastercard constraint or is Standard Bank making this up!!! Either way, my credit card is useless to me for international payments. Maybe I should just now go to a different bank.