Hi @Akncftc,
When you have Flex subscription, you will be charged at the end of “your month”. Such a month ends about 30 days after you originally started the subsription. So e.g. you started Flex on October 4th, you will receive an invoice around November 4th. The amount of the invoice will be withdrawn from your bankaccount a few days later.
The balance on your OV-chipkaart is not refunded automatically. Therefore you fill in a form on the website of OV-chipkaart.nl
The balance you ordered online will be put on your card at the next NS check-in, but you can get it back at a service desk https://www.ov-chipkaart.nl/en/service-points-finder (select Balance refund).