If you grate has burnt out then this may either be due to long term responsable use as the grate is a part on a stove that will wear out, but it is often to do with misuse of the stove.
A burnt out grate is often caused by burning coal on the stove and burning it too hot.
That means loading the stove up with coal and then opening the air vents up, especially the bottom air vent.
This can happen if the stove is not as large as it should be and is therefore being run at full blast to try to get as much heat out of it as possible.
So do not burn coal this fast. If you are pushing your stove to get enough heat out of itthen consider upgrading to a stove with a higher output or installing another stove.
If you burn coal and let the ash build up under the grate then this can also damage the grate as it makes the grate very hot.
Keep the ash pan fairly empty - empty the ash into a metal container / bucket when it is hot, not directly into a bin.