Pension fund data breach

Received a notice of breach including Corebridge Financial that included PBI. They want me to send my social security number to enroll in the free monitoring service. I tried to do this by phone as I am not comfortable in mailing out my info. They were supposed to put me on a call back list— said it would take awhile. Haven’t heard back. Can’t talk to someone who l owns how I should proceed with Kroll Monitoring services. Not sure what to do. Should I send info through the mail certified? Would that make a difference?