Sorry to hear about your troubles, it sounds like a frustrating series of problems. When my motor died I was on a fairly smooth strectch of tarmac. The indicator lights stayed on &, later, I discovered that power stilled flowed to the motor and without load - wheel off the ground - it would spin under power, but nowhere near the rpm it should be spinning and no hope of turning with me on the bike.
In my 900 odd km of commuting I've hit some pretty nasty bumps, but not enough to lose control like you describe. My guess is that repeated thumps have caused a stress fracture that finally gave up. Actually it was pretty bad timing cos I'd just smoked a lycra clad guy on a regular bike and then had to suffer the humiliation of him passing me.
Interesting - thanks. Mine sounds different as it is completely dead, with wheel off the ground, wheel already spinning, etc - no noise or anything. A guy on the pedelec.co.uk forum was pretty sure that means its electrical not mechanical (ie the controller).
Bad luck on your timing! I use my bike for commuting in London along one of the main routes and there are dozens of road bikes going at 20mph+. With the Tongxin, for a few short days, I had their measure! But good luck on having support from a local dealer. You may have paid a mark-up for that but you are getting value for it now. Hope you're fixed up and back on the road soon!