Audi a6 quattro 2001 coolant disappears, engine overheats and white smoke comes out

Hi All, Few days ago I was driving for 20 mins after starting the car. Then all the coolant just leaked on the street. And I filled up the coolant container and when I arrived in front of my house after 10 mins of drive, it spilled all over the ground again. I then put stop leak in the container with coolant and followed instruction. Engine still was over heating and coolant disappeared this time did not spill all over the street. I then took it to the garage, but before I take it there I had filled coolant container again and once I arrived at the garage the coolant liquid was gone but I do not see it leaking. And engine eventually started over heating. Mechanic said the Radiator hose that takes to the expansion tank needs to be changed and that's the problem. But auto part stores were closed it was a saturday and he cut the current hose a bit and put some coolant liquid and stop leak and told me to see if it works out. When I reached my house coolant liquid disappeared again and engine was over heating. The day after I put some coolant liquid but did not drive and after few hours it disapparead but no sign of leak or it didn't spill on the street. IT CAN'T BE MAGIC CAN IT????