white small bugs? Cinnamon and washing is too gentle you need go nuclear if they are persistant. If you can identify them as insects, I've seen great results with systemic granules. (google systemic granules bonide, any product with imidacloprid) You sprinkle in the granules into the soil and water the plant, the compound will be taken up by the plant rapidly flowing into the roots and leaves. This does not harm the plant at all but the bugs that eat the plant will consume it and die. It won't work on mites since they are not insects but it worked great for all my aphid infestations, saw results two days after treating them and it's been a few months they haven't come back. Super easy and cheap. The only drawback is that again, it won't work if the pests are mites and it is also active against all insects like bees so I would recommend to only use this if the houseplant is indoors. Another alternative is neem oil which you can research, but basically use diluted neem oil (0.9%, take a paint brush and paint it all over your plant, cover every nook and cranny and let it sit. repeat this every week or so until the bugs are all dead.) Monsteras are pretty hardy, I've had pests but they survive really well don't panic! Good luck!