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I imagine you are not in the US so you would not be able to get ahold of either Affresh tablets by Whirlpool or a product for cleaning spa tubs called "Whirlout". I hope you can get some liquid chlorine bleach, some white vinegar and some clean rags. What you'll need to do is to put the rags in the machine and run it on as hot a wash cycle as possible with at least 200cc of liquid bleach. The rags will insure that the bleachy water gets all around the inside of the drum. Then put about the same amount of vinegar in the rinse portion of a cycle or just run a rinse/spin cycle with the vinegar.
To prevent this in the future, leave the door open when not in use and minimize your use of detergents, you would be amazed at how little detergent these machines actually need per load.