First you need to find a different shop...this one is clearly taking advantage of you. 500 dollars to replace a bottom bracket after a couple of months riding is outrageous. Did they replace the crankset too? or just the bottom bracket? If you had really only ridden it a couple of months from the date of purchase and the bottom bracket was loose then the I would argue that it was an initial setup problem. And then another 100 to replace bearings 4 months later? Either you are a beast of a rider or you have the most expensive but sh*tiest quality bottom bracket on the planet.

-j