Green/white mold on phalaenopsis roots

[Cloudmaker]

Hi everyone,
I have a problem with 2 orchids. Everything started when i noticed greenish/white'ish spots inside the pot. I couldnt have overwatered them because I water only when they are completely dry, checking freequently, etc. Plus the pots were large enough to let air through. My sister told me that maybe the substrate was moldy when I bought it, because this is frequent issue. She suggested repotting and pouring the substrate over with boiling water, which i did. She also suggested to spray hydrogen peroxide 3percent on the roots, which i did as well. And of the orchids go to the new pots and new media. After couple of days here is the moldy spots again, both on the substrate and roots... I mean how and why? What am i doing wrong? What should i do.. i have no more substrate and pots to replant and everything is closed due to pandemic... Eshoping sucks at this point. Any thoughts?