+1 to the posts above. If you have some knowledge of electricity and have a volt meter then you can start troubleshooting yourself. After you have unplugged the cable from the car and plugged it in again check for change. If the same, then reset the breaker. Now check again. If no change, then disconnect from the car, unplug the HPWC from the 14-50 plug and check the voltage across the 14-50 outlet. If you have the 240 volts then the problem is with the HPWC. Remove the covers and start looking inside for any visible damage. If none, and you are handy with a volt meter then you can plug it back in to the 14-50 and look for electricity in and out.
It is at this stage that if you are not comfortable around electricity then you get an electrician to take a look. I doubt it is the car, but if all else fails, find another HPWC, or even a J1772 plug to test charging. A Supercharger will not help as it does not use the on-board charger. If another HPWC or J1772 also gives only 120v then take it to a Service Center as you have a charger problem. If you do get 240v then the problem is your HPWC. Your electrician may be able to find and fix the problem, maybe not.
Good Luck and keep us posted on the solution.