Thanks for reaching out on the Community!
If your account has reverted back to the free service and your attempt to pay has not been successful, the system will not try to take the payment again.
If your Spotify payment is marked as 'pending' on your statement, it might not have gone through successfully. When you submit a payment, your bank puts the funds aside as ‘pending’. If the payment fails, the pending status will expire and the funds will be returned to you.
When you have the funds on your account to start the new plan, you should be able to subscribe again without getting charged twice.
Hope this info helps!
Help others find this answer and click "Accept as Solution".
If you appreciate an answer, maybe give it a Like.