All journeys you made before you change your season ticket will be charged as Dal Voordeel. All journeys you will make after you change your season ticket will be charged as Dal Vrij.

If you change your season ticket during the month, you will be reimbursed for the costs of the old season ticket for the remainder of the month and you will receive an intermediate invoice for the new season ticket for the remainder of the month. In your case, for example, if you were to change to Dal Vrij today, this means you will receive back a few euros for your old subscription and pay about one third of the monthly costs for Dal Vrij for the remainder of this month. (Here you should read ‘the remainder of the month’ as ‘the period until your next regular invoice arrives on the 6th’.)

Hi Tochjo,
If I have made journeys with the Dal Voordeel abonnement, say 150 euros (incl. the abonnement price) and I change it to Dal Vrij (107,90) today, will I be charged 257,90 euros later when the next invoice comes?

Yes, you will pay the season ticket costs for the next month (6th November until 5th December) and the travel costs of the past month at the same time. For these costs you will receive an invoice around the 6th of November. (A little less than the 257.90 euros you mention if the 150 euros include the season ticket costs for Dal Voordeel for this month, seeing as you paid those costs in advance.)

If you change your season ticket today, then you will also receive an intermediate invoice in a few days, as I mentioned, for the season ticket costs for the remainder of this month (25th October until 5th November) of about 30 to 40 euros (since there's about one-third of the month still to go until the 6th, with a few euros subtracted as reimbursement for the Dal Voordeel season ticket you paid too much for in advance).

Alright, Thank you so much for your help! Have a great day!