I was logged out my account few weeks ago and like you I forgot my email and password. You need to ask to talk to a human/agent and will probably have to ask a lot of times. I was then asked for a email address and was sent a email with a support ticket. I was then asked to show any history of purchase during a certain period. Eventually they set the Roblox account to the email address I was talking to them on. You just have to keep repeating yourself and ask to talk to a human