First question: DO YOU HAVE AN INVERTER?
I will get to the Y/N part of that later.
I gather you have checked your main circut breaker box and any and all GFCI's in the RV.
Now This is in 3 parts.
Part 2: If the answer is YES (IF NO skip to part 3)
Find the inverter's breakers, These will either be ON the inverter (many are) or like mine in a 2nd breaker box somewhere other than where the main is, or in a few very rare cases right next to the main or in the same box. Odds are that's where the problem lies.
Part 3: I do NOT recommend plugging a 1500 watt heater into an RV outlet.. with the POSSIBLE exception of the washer/dryer outlet if so wired.. The reason.. Most RVs now days are wired with "Quick Box" type outlets. You pop the back off, Lay the Romex cable in and "Punch it down" into a couple of slots inside the box.. Very poor, connection, Very small contact area and when you start drawing double digit amps (1500 watts is about 12 amps) the things get hot and bad things happen.. I had "Hot Wire" smell (IN itself not dangerous but indicative of a pending response from the Fire Department) so I shut mine down and did a bit of er.. Editing. (more on that in a few words) Some others have had wires burn in two. and dead outelts just as you now have. And what is worse. The damage might be "Up stream" of the outlet you plugged into.
I have also burned a connection in my inverter junction box and one other flexible to hard core wire connection.. In both cases I re-did them using better than wire nut technology and no problems since.
now on my coach due to the placement of the breaker box, this was easy, I did not have to "Rip up" walls or anything like that.
I put in two 15/20 amp duplex outelets (plus one simplex outlet,, Means only one plug in) in my RV. These are fed by 12ga wire, Each (Save for the simplex) has a breaker ALL TO ITSELF. no problems since.
The Simplex is special. it is on the rear A/C circuit.. I figure I'm not likely to use both heat and A/C at the same time. normally it powers a volt meter (Not enough current to light an LED) but when it gets cold I can plug a heatr in ther.. The power line from the breaker box (main) goes to a "Break out" box (Outlet actually) that is outside the coach (in a locked compartment) and then a plug there comes back to a junction box where the "Split" is done, and then on to either the A/C or the Outlet. That way if I am on a 30 amp site,,, I can run a 20 amp cord as well for the A/C or Heater (And yes that too is 12ga) Works great.
Home is where I park it!