Frustrating, ain't it? Don't fret. It seems there's a bug in the mission's design. But just to be sure you're as good as you think you are, here's what you should have done by now:
After the helos have flown in and done maximum damage to enemy ground forces and armor in and around Chapoi, make sure there are no enemies left on the outskirts of town. Once you're sure, you'll have to head into town and eliminate any remaining forces. You'll most probably find one or two Russians left there.
Now, if after doing all that nothing seems to move, you've most probably come across the mission bug I originally mentioned. What should happen is that a US M113 APC should be coming into town from the north to help you mop up. Once you approach it, the mission should end.
It seems however, that the trigger to get the M113 started and driving into Chapoi isn't working. So, if you don't see an M113 heading into town, walk along the road leading east out of Chapoi and head towards an area marked on your map in green as friendly forces. You should find the M113 just sitting there doing nothing. Wake up the driver by lobbing two grenades or by firing some rounds at the vehicle and then wait around for about a half a minute. The M113 should then start heading into Chapoi and the mission should end successfully.