Problem with Confirming My Identity

I would like to apply for self assessment and went through all the process of opening my Gateway account. However, I got an email informed me that my information submitted didn’t match with the record in HMRC. I would like to know what information I should give, and how, to confirm my identity? I tried to call different lines but not any adviser can help me to sort this out yet. What can I do?

Hi,
Please contact our online services team who should be able to help with information you need to confirm your identity.
Technical support with HMRC online services
Thank you.