I was banded in July 2009 and lost about 40 pounds up to christmas and then I just felt no restriction at all. My doctor then moved to another state so I needed to see a new doctor who ordered a sip scan and found that the band had undone. My first doctor then rebanded free of charge and I am now in week 4. They gave me a fill of about 3ml and I feel that I need more. You paid for this surgery. Dont just let them push you around. If they wont fix it then threaten legal action. You have rights!
Also I have never heard of a band slipping cause you lost too much weight. My sister lost 180 pounds , is pregnant now and even without the fluid she still feels restriction. I think they are just trying to bully you.
I hope it all works for you. I do understand you frustration... when everyone else is losing weight around you and your weight just stops. I was too scared at first and it took 6 months to own up that I didnt feel restriction cause I felt like a failure. You are not the failure, the band failed you !