Cancel subscription with little to no information.

My son, when he was at school, had a creative cloud (student?) subscription. He finished school over 2 1/2 years ago. We recently just saw an AUD $871.07 charge on our credit card, which turns out to be a subscription renewal charge. How do I cancel this?

My problems are:-

1. My son has severe depression and getting information from him about anything is a major challenge. He just shuts down when stuff like this comes up.

2. He has no access to his former school email account (Presumably deleted by his old school). This email would have contained all the original subscription serial number emails etc.

3. The program was installed on a PC that has since died (will not go past BIOS), so I have no access.

Where do I start? All I have is the billing information from American Express.