Hey Victor, 

Alexandra from the Miro Support team is stepping in for a moment. 

I'm afraid this is technically impossible to detach a bank card from an active Miro subscription, I am so sorry about that. However, in your case, we could remove the card data from our billing provider's side manually if you set the subscription to cancel on your side. 

​​​​​You can cancel the subscription at any moment (the subscription will be active till the end of the paid period). Please go to the Account Settings > Billing:
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Then click Cancel subscription:
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After that, please, kindly submit a support request and we will remove your credit card details: How to contact Miro Support

Does it help? 

Please, let me know, if you have any questions! :) 

Alex, Miro