Can anyone give me some advice about an electrical problem.

I have a new renter who called me up and said that his oven did not work. Neither the broiler or the baking elements heated up. I had not had any prior complaints but maybe folks don’t use ovens much.
When I took it apart I found the terminal block for the 220v had melted through on the black wire and was a molten mass on the red but still attached.
When replacing the block I noticed that, although it was a three wire (three prong) plug, it had been wired up like a 4 wire (four prong) system but with the additional copper ground from the neutral as well.
The difference seems to be that on the 3 wire the neutral is grounded from the terminal block directly to the range while on the 4 wire it attaches to the terminal block only and a ground wire goes to the range. What I have is a neutral that ties to the terminal block and then is grounded to the range but the ground wire from the plug is also attached to the range through the tab.
I am not sure how it is wired in the plug and probably need to check but would having both the neutral and the ground connected together have caused the burning and melting? Would it have worked for a while before burning out? What else could have caused it?
Should I wire it in as a 3 prong only and cut off the ground where it comes out of the flex conduit?
Any help would be greatly appreciated.