I can no longer log in to my Minecraft account, neither via Luncher nor via the website what should I do?

As I have already read in the question above, my MC Acc is no longer working. Do you have an idea what I can do or who I need to contact? There I have to enter a valid email address but my email address is valid!

please suggestions…

Maybe you made a typing mistake or there are spaces in front of / behind the addy. Simply place the cursor in front of / behind and the backslash / remove. Press button. Sometimes it works.