2000 Daihatsu Cuore Bad white smoke

Please can you help me, my car started smoking white smoke from the exhaust so my mechanic told me my rings have gone, I sent in my block and it was reboared and I had to buy new pistons and rings. I also bought new valves and valve stem seals as the compression was not right. The mechanic checked that the rings were the right size and that the pistons fitted properly. When the pistons were put in he checked to see that there was no play on the pistons, they were perfect. Then engineers fitted the valves and seals and my mechanic reassembled the motor. When we started the engine it is doing the exactly the same thing - thick white smoke pouring out the exhaust and you can smell the oil, in fact it has got worse, I don't know what to do as everything has been replaced with new parts, even the engineers cant understand what is going on.