How do I factory reset my AWS Account or how do I delete all the services and their resources back to having a clean slate?

Hello.
What error occurs when I try to delete CloudFormation?

I think that using aws-nuke will help to delete most all resources.
https://docs.aws.amazon.com/prescriptive-guidance/latest/patterns/automate-deletion-of-aws-resources-by-using-aws-nuke.html

There is no button in AWS that resets the account, but you can delete all of your resources manually. Here are the steps on how to delete a stack from CloudFormation:

Go to the CloudFormation console. In the navigation pane, choose Stacks. Select the stack that you want to delete. In the Actions menu, choose Delete Stack. In the confirmation dialog box, choose Delete. Here are the steps on how to delete an application from Lambda:

Go to the Lambda console. In the navigation pane, choose Functions. Select the function that you want to delete. In the Actions menu, choose Delete Function. In the confirmation dialog box, choose Delete. If you are still having trouble deleting these resources, you can contact AWS Support for help.

Have you tried steps in this trouble shooting document ?https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/troubleshooting.html#troubleshooting-errors-delete-stack-fails

Have you checked your role, if you have permissions of deleting a stack? Also do you see any error in the events tab?