How are the turbos failing, that should point to the problem. Sounds like either they are not very good turbos (rebuilt poorly) or there is another problem with the engine that is affecting the turbo (oil starvation to turbo, grit in the oil to turbo etc.)
If it is a Kia garage Customer Services need to be made aware.
If its not the garage you are using are clearly a bunch of cowboys who have no idea what they are doing.
In truth I find it hard to believe any garage would actually fund 3 new turbo's when they can only charge for one so tell us more about the garage and where they get their parts.
Got car back after 4 weeks. The garage were rubbish but Kia UK sorted me out a hire car for free so that was good.
I don't have a list of all the parts, the garage said i need to email head office, even though they fit them. Odd. Anyway, it had a full engine strip down, new headgasket, oil pump and some other bits.
Engine seems better than ever! It always had some turbo whine but none at all now. It'll take time to get my confidence back in the car and I still might get rid but pleased with the Kia warranty.