This is a common problem among elderly people who are easily confused online. Sometimes, they're unsure about what they're doing or may press things by accident.
Almost always, they'll figure it out before they submit payment, but not necessarily before they indicate that they're ready to pay, which is why you receive those emails.
Fortunately, this isn't a technological issue; it's just an unfortunate problem with seniors/illiterate visitors.
When this increases, as you've experienced, it's a sign that your domain is receiving new traffic from something, such as another service using a similar (domain) name. You can
track your visitors with Google Analytics and search Google to investigate the cause.
In short, there are a lot of easily confused people online, and sometimes, they land on your landing pages.
We plan to add a "Reduce confused inquiries" feature for domains that experience this issue, so you can enable it if you choose. It'll introduce additional prompts and roadblocks to confirm that they understand what they're doing and stop them if they don't.
That will help a lot and be the first of its kind.