To keep your home free from flies there is a special product on the market which most hardware stores will stock.  There are various brands on the market but it doesn't really matter which one you choose as they all work in the same way.

The product resembles a transparent glue but a glue that takes nearly forever to dry and so remains sticky for days on end.  It also contains an ingredient that attracts the flies to it but once they touch it they will become stuck and eventually die.

You have to get some long bamboo shoots (stripped of their leaves) or any long stick that you have lying around the house like maybe an old broom stick.  Put a hook in the ceiling of the terrace that you have just outside a door or window of your house and another hook at the end of the broom stick or bamboo shoot and hang it up.  Now you give it a generous coating with the glue product and that is it.

Any fly that is making its way towards your door or window and hoping to come in will first be attracted to the glue and pay a visit to this before entering your house but alas for the fly he will never end up getting into your house as he will have become stuck to the pole.  And just as this particular fly ended up like this so too will hundreds of other flies that are trying to get into your house.

After about a week you will see that your broom stick or bamboo shoot is completely black having been covered with masses of flies and dead at that, so you will have to hang up a new one.

This really works and is a relatively cheap solution.

I don't like killing anything but sometimes you just have to when other creatures try to invade your space.  As I always say to my husband - in our home we live me and him and nobody else and that includes flies.