Recently i got new battery fitted to my 6n2 gti and after a week kept going flat took to halfords for test it  was alternator at fault put recon alternator on  after few days same again bought new alternator yesterday and flat again after a day was reading 13.2 when fitted yesterday any help on this as its driving me nuts 

Have a read of this

 

Could swapping wires red/yellow on stereo cause drain problem when I bought head unit from  Halfords they said it wouldn't make any difference but now I'm not so sure 

A radio memory supply current is very low so shouldn't flatten a new battery, if you carry out the checks listed in that link, that will eliminate the alternator as the cause for draining the battery.

 

Have a look at this also

Similar problem to yours, and the fault finding methods will be the same for your car

I'll look into it cheers