Last year Amazon announced they would start running ads on Amazon Prime Video starting in early 2024.
If you are still subscribed to Prime, contact your credit card provider and ask for chargebacks extending back to March 2024. This should be possible because Amazon violated their customer contract and is no longer providing the service you originally wanted. They shouldn’t be charging the same price while providing a lower grade of service. You deserve a refund.
“To continue investing in compelling content and keep increasing that investment over a long period of time, starting in early 2024, Prime Video shows and movies will include limited advertisements.”
Source: Amazon shares an update on Prime Video, introduces limited ads