What are you using for the default? 

login: admin

password is either password or the last 8 of the serial number

did you try them both? 

have tried both, neither of them worked. i have logged into it before and it was just admin and password

now after multiple attempts at hard resetting it says that is not the right username and password

yes ive made sure im holding the reset button long enough yes ive tried the 30 30 30 method. same result cannot log in no the right username/pass

As you mentioned, you unable to login GUI portal with default username as admin and password as password. Also I understand that you already tried with reset multiple times.

I suggest you to follow the steps and try again to login the GUI portal with default credentials.

Disconnect all the cables from the modem including power cord.

Wait for a minute and reconnect only the power cord, hold the reset button for 30 seconds by using paperclip.

After 30 seconds, release the hold and reconnect all the cables back to the modem.

Once led light solid, log on to 192.168.0.1 and use the default credentials as admin (USERNAME) and password (PASSWORD).