Made new pokemon go account using same google account accidentally and cant get back to old one
Solution 1:
I know you don't want to hear this, but your old account is likely gone.
Occasionally, a bug will affect player accounts causing them to be reset back to zero or deleted altogether. From this point onwards, the only way to keep playing is to re-create the account.
As you're certain that you're using the same Google account, the only reasonable conclusion is that your data is gone into the digital ether.