This is Rae from Shopify. Thanks for starting this thread.
I understand the importance of getting your bank account information updated so you can receive your pending payout. There are a few different methods we recommend trying to resolve this, and I'm happy to help out with these.
As a starting point, if you have a paper statement from your bank, or a void cheque, these may contain your old banking details. Equally, if you have online banking set up, your old account details may also be listed here once you log in. If these options aren't available to you though, we do recommend contacting your bank directly to have them provide your old account information to you. Once you have this, you can update your banking details directly in your Shopify admin under 'Settings > Payment providers' by clicking the 'Manage' option under 'Shopify Payments'.
However, if you're still not able to obtain your old banking details after trying the above options, please let me know and we can proceed with the next steps needed to reach a resolution.
Keep me posted on this!