At this time I would go with stronger antibiotic like Silversulfadiazene. Repeating the treatment that failed (formalin-malachite green soaks) is probably not going to work well . Also, please ensure there are no sharp decor were frog could injure itself in tank.
Another option is to get Maracyn Plus (effective against gram + and - bacteria) at your local pet shop fish section and treat frog with it. Just follow the bottle's directions; but be careful you do not overdose. What I do is prepare a gallon of treated dechlorinated water and use it to replace the whole volume in the frog's enclosure water section as needed. That way the frog is exposed to medication all the time it's in the tanks water. Good luck!