Why can I watch netflix despite being terminated?
Because the termination does not take effect immediately but only at the end of the month or the billing period
Either the month isn't over or you haven't quit
When did you quit?
I don't know the exact terms, but with most providers you can't cancel for the current month, but only for the next.
I guess because the rest of the month (or the time you paid in advance) is still available.
But there it can only reactivate because I have already given notice and checked
The cancellation will only take effect when the paid time has expired. So if you e.g. You have a subscription for the 15th of the month until the 15th of the following month, you paid for this period.
Then the current month is not over yet.
E.g. If you start your subscription on the 10th, cancel on the 20th, you can still use Netflix until the 10th of the next month.