I don't know what you can do about the past meetings, but next time you have a meeting scheduled, inform your PO that you officially request the terp that you are legally entitled to. Then if one isn't at the meeting, you need to decide if you refuse to do anything but sign or if you just give in to him. If you give in you'll have a harder time getting the terp because in his mind you don't really need it and you've "proven" that to him.
You should have some legal representation, even a legal aid attorney should be able to find a terp for you and be sure your rights are protected.