I used to fix computers long ago - I know very little about cars but I count a total of 4 alternators including the original - I have never had an alternator replaced and I don't know anybody who has.
It may not be like this on your car but an alternator used to be fed with an exciter current to make it operate properly - the wire coming from the Battery Not Charging light. When the voltage from the alternator matched the voltage on the exciter wire the lamp goes out.
Trouble is - if the lamp fails or if the exciter wire has a dodgy connection the alternator would not produce many volts - the battery would not charge and you would never know about it!
I suspect that all your alternators were in good order - a garage makes more profit on a new alternator rather than fixing a loose wire and you have had the misfortune to need three - I smell a rat.
As for your other faults I can offer no help at all - perhaps the anti-pollution warning is genuine.
Whatever the faults may be it will cost you money to get them fixed but I would advise you to find a different and reliable motor repair specialist - I have no faith in the people you've been going to.
Nevertheless...
Good Luck...
August 2015