So the new timing belt broke after 3 days?
First are you sure that it was installed correctly? The timing belt tore or did it slip? They are made of kevlar fibers and it's very difficult to tear them. More likely there's another problem that caused it to come off and then it got shredded.
There could be a problem with the camshaft, crankshaft, head, or some other problem. If the head was replaced without inspection it's possible another valve broke because of damage from the first time that was not detected. Get an all new head and inspect the crankshaft sprocket, or have someone else double check your work.