Peugeot 206 everything usually electrical

You tried LOAD testing the alternator ?

Not yet, just went and tested it again and now it doesn't appear to charge any more as once started it dropped to 11.7v, already ended up paying out too much on this temp car repairing things it just doesn't seem worth it anymore as just after I mot it last Nov to sell I let my son and gf use it and the brakes failed on them, had to have all new rear cylinders and pads, so maybe the thing can go to the scrappers now as hubby won't pay out anymore on it lol

And it now also needs a new post cat o2 sensor too as it's thrown that up as an error now

A lot of these " reconditioned " alternators are rubbish . You could check the wiring / connections at alternator and also battery connections and any earth wire usually from engine / gearbox to body .

Found out that the battery wasn’t the correct one and had fried the module inside the alternator ,guy replaced the burnt out module , funny thing was the car sat at my sons with a non working alternator for 8 weeks and the car started every day with it not draining , he also changed the o2 sensor for me as that failed , it just failed mot last week on 2 rear bearings,2 brake hoses and 2 front tyres , all was working well so was planning to get it through mot then tonight I go to start and the battery is dead again ,was going to sell it once it was mot’d as have my own car back now ,but can’t sell it with a fault so may as well just scrap the thing now

Never heard of a module in any alternator and of any 12v battery , even of the wrong type , frying an alternator . Usually an overcharging alternator due to a faulty internal regulator will cook the battery .I would be Load testing the alternator and checking the charging rate / voltage to verify the work carried out . Would be a pity not being able to get some return for all the money you have spent on the car .

Components inside an alternator ,
https://www.autoelectro.co.uk/alternators

He took the alternator off and to a place in Leicester called greens ,they have been there years , some old guy ,they did some test on it and repair them while you wait ,he gave me son the part which he gave me but we have since thrown it away it looked like a regulator was a rectangular with 2 metal prongs on that are soldered on to something inside alternator and it was all black and charred, he told my son it is when your battery doesn’t have the correct amperage Cca it puts extra strain on the alternator when cranking and over time causes this to fail ,he also said that if you have a dead battery to make sure it’s charged for a minimum of 8 hrs otherwise trying to start with a half charged battery will cause the same issue , before the repair when starting the car there was no voltage increase on the battery ,afterwards it went back to around 14.2 v .
I mentioned it to the garage when I took it for mot and they said that’s a new one regarding the cca of the battery and would remember that for the future ,so who knows

As suggested in first reply , the alternator was faulty . I'm an old guy also , lifetime running garages , as for the battery " theory " ....................... Like your garage , being polite " that's a new one " I can see what he is suggesting , with a low battery the alternator will charge higher but is controlled by the regulator and limited . But that's here nor there . You could sell as is , showing any prospective buyer the MOT failure and what is needed , but lowers the price . Also no guarantee on a car of that age and a private sale . You could advertise as described and I think you will get a buyer . Or you may just want to get rid of it , they are people who buy MOT failures and repair them . Best wishes whatever route you choose .