Wrongly installed shutters , should I pay rest of balance on invoice ?

[Charliescar]

Had shutters fitted on 20th Dec . Fitter did not install them into recess of window as agreed . I have this in writing.
However , fitters is saying that when I paid the deposit invoice ( so he would order shutters) it says on invoice that full payment will be made 7 days after him receiving shutters or installation, whatever comes soonest.
I have said I will not pay the rest of the balance until the work is done as agreed , to have the shutters fitted as far in to window as possible. This is in writing . He has only done this on one window ! There is no reason why he hasn’t fitted them line this , I think he forgot !
Should I stick to my guns and not pay until the work is done ?

Just to go against the other posters, you are liable for the portion of the work done correctly (although payment before the work may have even started is clearly an unfair term and surely can't be upheld)
The work not done you can withhold the cost of that, and if there is any further damage eg damage to plaster from fitting in the wrong place, he is liable for that.
As an example if you got him to fit doors, Windows and paint the rooms as well as the blinds, the bill would be a lot higher but you would still only be able to withhold the relevant amount which wouldn't change.
Also if he has underquoted you might end up having to pay more overall to have it put right by someone competent