Cannot access account, delete account, cannot remove SSH key, import fails without error message

I created an account at GitLab, and started importing a repository from Github, but after a while this somehow failed, and whenever I log in, it just sais “Error 500” and I can’t do anything with my account!
Therefore, I created a new account, where I wanted to push the repository from my PC, but I am not allowed to use my SSH key because it is already in use for the first account, which I am unable to access to delete, to due the “Error 500”… also, when I try to import the same repository from Github again, it just keeps saying “importing…” for a while, but in the end, I just get an empty repository with no error message to indicate what went wrong.

Considering I just started using Gitlab yesterday night, I am somewhat surprised I encountered so many different issues already. Is this typical of Gitlab? How can it be fixed (so that I can use my SSH key again, at least)?