Yair You made a pre-payment for 2 years of the Easy Money plan. This means you basically get a discount for 2 years for 8.99 Euros/month after that, because that amounts to the pre-payment you did. In exchange for doing this, you got a free Metal Card.
Now you apparently changed your plan to Easy Green. This is fine of course, but the monthly price of Easy Green is 17,99 Euros. Which means you now still have to pay the difference of 9 Euros/month to stay on the Easy Green plan.
You could've ordered the Metal Card while being on the Easy Green plan. Then you would've needed to pre-pay for 12 months of Easy Green and would've gotten the discount of 17.99 Euros/month for one year. But in the end, if you plan to stay with bunq for a longer time, this doesn't really matter. It all comes down to the same overall pricing: the Easy Money plan costs 8.99 Euros/month and Easy Green plan costs 17.99 Euros/month. You just changed around when you pay for it through the pre-payment.