In Colombia, the landlord has a legal obligation to maintain the property in habitable conditions, and humidity that affects the structure is a hidden defect or serious flaw. According to the Civil Code, you have the right to demand repairs or, if the problem is serious, to rescind the lease. The first thing you should do is document everything: take photos of the stains, keep the messages where you asked the landlord to make repairs, and if possible, get an assessment from a professional confirming there are structural humidity problems. This gives you legal weight if it goes to court.
My recommendation is to send the landlord a written notice (by certified mail or legal messenger) giving him a reasonable deadline, like 15 or 30 days, to make the repairs. Specifically mention that if he doesn't, you'll exercise your right to rescind the contract for breach of the landlord's obligations. If he ignores this, then you have grounds to go to civil court or a conciliation center in Medellín. Generally, if you can prove the defect makes the property uninhabitable or dangerous, you have a good chance of getting your full deposit back and not having to pay for the remaining contract time.
Ideally, you'd consult with a local lawyer before sending that notice, since they'll know how these cases work in your city and what strategy works best. Many offer free or very affordable consultations.