If your channel received 3 copyright strikes within in a 90-day period, then your channel will be terminated. You can still submit a free-form counter notification even if your account is terminated. You can do that here: https://yt.be/help/dHCP
Your channel was terminated because we determined that it was linked to a channel that was disabled for having three or more Copyright strikes. There’s more info in the email sent to you, including instructions on how to appeal if you think it's a mistake.