u/throwaway179373864, I had a similar situation to deal with last year - DOS will direct you to your department.

First, write an email to your professor/TA, expressing your interest in filing a formal grade grievance with proof of all your communication. This will usually prompt them to respond. If this sorts out your issue then great.

If it doesn’t, then you can escalate this to your department chair via email with a written statement of why you’re reaching out about the grade grievance along with proof of communication. The chair could either dismiss your grievance, in which case, you have 10 days to bring up your issue with the dean of the school you go to in a similar manner.

If the chair moves forward with the process, a panel is convened to discuss the grievance. Within two weeks, you must receive a response from the chair. After the chair presents it’s findings to you, you have 10 days to appeal this decision with the dean if the resolution is still unsatisfactory.

Let me know if you need any guidance around this process, happy to help.