Is there a for sure treatment for cellulitis?

Antibiotics. Cellulitis is a bacterial infection that involves deeper layers of subcutaneous tissue and can spread quickly, sometimes leading to life-threatening complications. Proper treatment with antibiotics, often initial intravenously then followed by oral treatment, is the appropriate way to treat. If cultures are available then that will greatly aid the choice of medicines.
Yes. An antibiotic or an antifungal can be used to treat a cellulitis depending on the cause of the problem.