Thanks for posting your query at DoctorSpring.com. I can understand your concern.
From the history you have provided, there seem following possibilities.
1. There is an underlying condition like diabetes or other immuno-suppressive illness.
2. It is misdiagnosed as tinea.
3. There it is an application of a steroid craven which is letting the fungus grow.
I would recommend that you send a picture of his condition to me if possible. Also i would recommend to meet your dermatologist to get a fungal scraping, culture and antibiotic sensitivity done.
Kindly let me know all your queries.