Hey there, Christine
Bo here from Shopify Support!
Thank you so much for reaching out regarding this. I am so sorry to hear that you have had such trouble with this. In future, to get support you can go to this page and click Contact Support you will be prompted to either login or continue without a store. Once you have selected an option you will be asked to ask about a topic. Search for your query and relevant help docs will populate as well as the option to proceed to chat, email or to schedule a callback when that option is available.
Could you let me know what error message you are receiving when you try to change your banking details? Is it telling you that the banking details you have entered do not match what is on record? If so, I will need to reach out to you via email to authenticate you as the owner of the account.
Looking forward to hearing from you,