Bankart repair 4 months post op stifness please help!

Hi, i am a 20 year old male i had a open bankart repair performed 4 months ago, i was in a sling for six weeks after which i was statred on R.O.M exercises, 12 weeks post op should have been sufficient timefor me to regain my R.O.M according to the surgeon but i am now 16 weeks post op and i only have 50 % R.O.M. Can someone please tel me how long can it take to get my R.O.M back to normal.
Thank You.