How to get a 3 month visa for Vietnam?

I've been to Vietnam in the past, and always am given a one month visa. There are some volunteer programs I'm interested in doing in Vietnam, but most of them are longer, like 3 months. In the past, I've only gone for 2 weeks. I can't figure out how to get a 3 month visa???

I've tried contacting the Vietnamese embassy, but the don't seem very organized. They're mailbox is always full on voicemail, they don't call back, no one speaks much english, and they ignore emails. It was hard to enough to figure out how to get a 1 month visa in the past and 1 month seems to be the limit....

...if you can help, that would be great.

Thank you!