I just wanted to chime in to say that form 8655 is a Reporting Agent Authorization. Our clients sign form 8655 to give us the permission to file and pay certain returns on their behalf. This form does not give us authorization to speak to the IRS on the client's behalf. Your company likely signed form 8655 to allow ADP to file and pay certain returns, but that form did not give them the authority to discuss this matter with the IRS. The bottom of form 8655 states the following:
The authority granted on Form 8655 will not revoke any Power of Attorney (Form 2848) or Tax Information Authorization (Form 8821) in effect.
I think you're on the right path with using 8821, especially with the other answers here combined with their experiences.
When we take on a new client, they will sign form 8655 to allow us to file their payroll returns, and they sign form 2848 to allow us to speak to the IRS on their behalf.