I received warranty repair for a company car, but the outsourced workshop is threatening to cancel the warranty..

Hello. I am an ordinary office worker working in Daejeon.
A problem occurred with the transmission of my company vehicle, so since it was still under the manufacturer's warranty period, I left the car at an official manufacturer service center in the Chungnam region on November 5th.
After the repair was completed, I requested a "maintenance report" for vehicle management purposes. In response, the service center told me, *"We only handled the removal and installation of the transmission, so you must contact the outsourced workshop that actually repaired the transmission directly to get the report."*
So, I called the representative of the outsourced workshop I was directed to and requested the issuance of the maintenance report. However, the workshop representative refused, stating, "We have no obligation to provide maintenance reports."
Perplexed, I argued with them, asking, "Please tell me the official way to obtain the maintenance report," but the response I received was shocking.
"If you keep acting like this, we will cancel this warranty repair and process it as a standard paid repair."
I informed them that the call was being recorded and asked them to mind their words, but they simply said, "Do whatever you want," and hung up.
I proceeded with the repair legitimately under the remaining warranty, so hearing such an unfair remark—that they would "cancel the warranty repair and change it to a paid service" just because I requested a report—leaves me feeling utterly hollow and bewildered.
I have requested an official apology and the issuance of the maintenance report from both the manufacturer's headquarters and the workshop in question, but I have received no response so far.
I would appreciate your advice on how to respond moving forward to rightfully receive the maintenance report and an apology.