The same happened to me. I am sorry to tell you that you are going to have to create a new account, because if you did not combine the link with the old platform you have lost everything. I will clarify my case, if you are an example.
I had a 4 character long alphanumeric username and password for the old platform. They sent and warned that they were going to migrate the old platform to the new one, and they sent a link, where I could see my tracker on the new platform.
But I did not pay attention to him for the first time, I kept using the old platform until in December of last year, there was a moment when he didn’t let me in, he could only try to enter the new platform.
But he did not recognize my credentials, nor did he agree. Now the minimum password must be 6 characters in length, so I had to create a new account with your password again