Hey @Lior, you can check the history on the GCP console to know your activity on the google cloud platform. That would list all the actions performed from your account, for instance, any VM that you have started, any service that is requested, any storage resource you utilized, etc.
There might be a possibility that you would have created a VM or used a resource but didn't cancel it or shut it down. In this case, Google will charge you for all the resources that u hold in the background. In such a scenario, you don't have an option but to pay for whatever resources that have been active in the background.
In case you want to cancel your google account, have a look at https://cloud.google.com/storage/docs/faq