What they all said!
My bike had some issues with the derailer and shifting... for MONTHS and MONTHS!
I kept taking it back to the shop... and they would keep it and then say, "It's fixed". It wasn't fixed.
I honestly thought my bike could never be fixed. I had seriously given up hope on using the big ring ever again.
Then, a guy on a ride took me to see his mechanic. Guess what? My bike got FIXED RIGHT! It took a few more months of adjusting the derailer to get everything just perfect, but my bike finally shifts properly and I can use ALL the gears!
I would suggest taking it to another mechanic.
"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather, to skid in broadside thoroughly used-up, totally worn out, and loudly proclaiming: WOW WHAT A RIDE!!!!"