Are you overwatering? Very most soil will encourage the growth of gnats. Let the soil dry out as much as possible. Of course there are many different types of flies so I chose to talk about one type which very well may be not the type of fly you are seeing.

do you have a fruit bowl? I sometimes find fruit flies especially if some fruit has gone off unnoticed in the bowl.

You might try putting grit on top of the compost in your house plants.

Find out what is drawing in the flies. The flies are decomposes so. Hang up some of that sticky fly paper.

Did you use garden potting compost? as they tend to have those tiny flies in the soil, best to have Houseplant soil.
I had tiny flies at one time and used house fly spray and ended up with loads of dead ones and keep using it for months so in the end I got rid of the soil, washed the roots & replanted my plants in House Plant soil :o) no more flies now :o))

Thank you so much, I think it is a soil problem as it has been in the pot a very long time.
By the way it is a rubber plant we have had for many years we cut it down last year took 3 cutting which were very successful family and friend were delighted to get a gift.
Again thank you all :)

Hope they didn't get your flies too LOL