You have nothing to lose by appealing. I mean the account is gone. You might as well appeal it.
Be clear, inform them about the company you used to run the test, be ready with any correspondence or invoice related to it.
Google Play has a very defined Internal, Closed and Open testing policy. Did you follow it properly?
https://support.google.com/googleplay/android-developer/answer/9845334?hl=en
There are very specific requirements for new accounts as well -
https://support.google.com/googleplay/android-developer/answer/14151465?hl=en
Was this the mandatory pre-release close test? Did you answer the questionnaire properly?
Are you using a reskinned app? Did your testers flag anything?
Does your app require permissions that may not be deemed necessary?
Do you have a history of banned accounts?
What service did you use to run the tests? Was it a legit service? How were the tests setup?