2013 Jetta TDI won't start

One day our 4 month old Jetta TDI didn't start. Nothing, not even turning over. It just
had an oil change, assumably a week earlier. The dealership said it was a faulty crank
shaft sensor. That took 4 days, then they call to tell me my starter is gone too. Only
had 12,000 km on it. I am on the side that the oil change may not have had oil or not
enough. Just my gut feeling. They are not being too forward with their answers as to
what the cause could have been.