It sounds like the Title Co. was not aware that the tenant prepaid rent and just prorated the current rent for the month of closing, so agree if they had no knowledge of it, would not have ever gone on the settlement statement as a credit to the buyer and they likely will not do anything post closing to help obtain those funds. I am guessing that the tenant may be short on funds to pay twice for Jan, until reimbursed by the old owner, so would first make your case to the old owner who has the funds you are owed and certainly hope once reminded of that will refund them. It sounds like the tenant has solid evidence their check or auto payment was received by the wrong party.
If the seller isn't responsive, then do like the idea of telling the tenant you tried, and see if they can get some free legal assistance from a tenant resource center.
It is a good reminder as closing approaches to ask the seller to keep tenants updated on the pending sale and when ownership is scheduled to change.