Welcome to the forum! You should be able to get some good information, lots of great people here. Hopefully someone with the same model will chime in to trouble shoot. Could just be a matter of technique. Coal has some learning curve and the same rules don't apply if you are used to burning wood. A couple key points, coal needs air coming up thru the grates to get it to produce good heat. Try letting in combustion air from underneath the grates, cut back any air coming in over the fire to a minimum. Hopefully the grate system doesn't have any way for combustion air to get around the grates instead of going up thru them.
Draft is also very important. You may need a manometer to check it. Most coal burners here have one permanently installed to monitor draft pressure continuously. Manometers are cheap and simple to install
ALSO, you must be able to shake the grates to clear ash from the coal bed. Don't be afraid to shake them vigorously, short choppy strokes don't reef on anything. If a piece of coal should lodge in the grates, let it burn or use somekind of poking tool to dislodge it from underneath.