Unable to get access to my Gmail account

Though I remember my username as well as password ,still unable to login my account.If i am trying to open it the other way by getting the verification code on my mobile number then also after entering the OTP ,it is not helping me to go further else it is just asking more verification questions which are i am unable to recall.I have several times mailed the customer help for my authentication still did not get any support.Please help ,i really need to retrieve my data.