error -1001 on iphone 6

I have an iphone 6 with UK Three provider as I spend half my time in Switzerland which is a "feel at home Country" and therefore free to call home and "all you can eat data" etc. My problem is that website and app loading takes an age and times out, sometimes with the error code -1001. I can facetime and get messages and emails ok, however buying a train ticket, looking something up etc is impossible. I have phoned Three several times about this issue and taken it to the Three shop. My phone works perfectly well in the UK but is hopeless here. Is it possible that the Swiss providers paid by Three are somehow keeping all the network for their Swiss customers??? Please help!! It is so frustrating, I have had my Three contract for about 8 months and have never managed to use a tiny fraction of my all you can eat data!