It’s likely the HR doesn’t know the process so will say no rather than help to find out. Good ones will help to at least give you contacts as many companies use agents for the visa process.
My advice is to speak with their Head Office HR. No company can deny you applying for your spouse in any case, but they are unlikely to pay for it unless it’s part of any employment offer. They need to only prepare supporting documents for you, then take them yourself to immigration.
The airline also has the right to refuse boarding, and they do keep checks on visas across ASEAN. Speak with immigration, find out why they denied you, see if you can sort it. Don’t risk losing money on a flight and being denied boarding let alone arriving at the other countries immigration.
Foreign journalists have a bad reputation here generally unfortunately due to the strict policy the government has on reporting on certain topics, and foreign journalists who have reported regardless. Don’t lose hope, but have a back up plan and good luck!
Can you not both come in on different visas, then meet with immigration once here if your husband plans to continue freelance work. It’s difficult to get the M visa now, but not impossible. You do need to be prepared to do something else if you don’t get it, as working in journalism without the right visa can end up in being arrested and all of you deported. That then will affect any chances of work across ASEAN with agreements that the government has in place now.