1999 Mercury Sable EGR flow insufficient- won't pass inspec

Engine Performance problem
1999 Mercury Sable 6 cyl Automatic

We've spent over $550 in the last week on this car and the problem is still the same the MIL stays on and even after we check the code at Auto zone and erase the code (as they recommended) it still fails inspection. The inspection receipt says CATALYST. EVAPORATIVE SYSTEM, and EGR SYSTEM are all not ready. We replaced the EGR valve but the code is still the same when we check at auto zone. We've disconnected the battery too as advised by some people. What should we do?