If your washing machine’s drum is covered in a greyish white coating it is probably caused by limescale. To remove it try adding about 20 gram of citric acid into the machine and wash on a 90 degree wash cycle with no laundry inside. You may need to try it more than once.
The best method is to put the washer on the 90 degree wash cycle and add the citric acid into the soap dispenser drawer whilst it is initially filling up. Let it fill for 10 seconds first because the first lot of water goes into the sump hose under the drum and is sealed off. Alternatively try buying a limescale removing product designed for washing machines.