Although I can sympathize with the story, this particular aircraft had been in their hands just a couple months. Its first commercial flight was just a couple weeks back. Maintenance isn't the issue here, clearly.
Fixing known problems as you learn of them is maintenance is it not? That's just as important as changing out the lubricants and checking that the working parts are working.
When you hear hoofbeats think horses, not zebras. A pressurization fault on the ground where the plane is not pressurized almost certainly doesn't hint at problems with a permanently installed door plug.