Either party can revoke consent at any time. If the customer can close their account at any time without notice, why shouldn’t the operator be able to as well?
The service did nothing wrong. They’re not a backup service, and if a customer ends up being more of a headache (either financial, emotional, or simply just time/attention) than the operator deems their custom worth, they have EVERY RIGHT to opt out of future transactions.
Furthermore, the customer explicitly agreed to this when they signed up. Even if they hadn’t, though, it is entirely reasonable for either party to the business relationship to be able to say, at any time, “this isn’t working for me, let’s stop.”
That’s how consent works in real life outside of business contracts, too.