Why do I even bother?!

I'm a bit fed up with it all today.

A few days back I got an urgent call from one of the families that I spend a lot of time with when I'm in Soroti. I stopped what I was doing and headed over to their house and it was explained to me that Joyce ( their 11 year old) was "very, very" sick. Thankfully it was not nearly as bad as they presented. Since that morning she had nausea and vomited several times. As she wasn't feverish nor did she have any other symptoms I just switched her from the porridge they were trying to give her to gator-aid and tried to teach a little about clear liquids, hydration, etc. I suggested they let her rest and encourage her to drink even if she keeps vomiting and I would come back and see how things were in a few hours. When I came back to check on her that evening she was playing with her little brother but said she was still nauseated. I gave pepto, confirmed that she drank all of the liquids I had given her and that she hadn't vomited again since I had been there and reassured them it was most likely a stomach virus. They asked for money for medicine. I ran through my whole spiel again. No fever. Just a virus. Needs fluids and time. Antibiotics would be useless for this and possibly make it worse. She was getting better and really didn't need anything. Thought they got it and headed home.
Several days later I got another call that the little brother had "collapsed" and was also now "very sick". I found a lethargic but fully conscious kid who was vomiting but had no fever and seemed to have exactly the same thing his sister had had a few days before. I explained why I wasn't overly concerned, gave them more gator-aid and prepared to leave. They stopped me and asked for money for treatment. I explained it, rather patiently actually, all over again. Stomach virus. No fever or other symptoms. Needs fluids and rest. No treatment necessary. They told me that actually with the other child they had taken her to a nearby drug shop and purchased some malaria treatment. I asked if they tested for malaria first (because it isn't malaria season and highly unlikely to be malaria). No, they had not tested first. They didn't have enough money. (This was said in an accusing tone. They had asked me for money and I hadn't given.) I asked how many doses she had gotten. Two. Out of the necessary six or eight for a full malaria treatment. But they assured me that she had only had "slight" malaria so they didn't have to purchase the whole course of treatment. She felt back to normal by the next day so the treatment must have worked and obviously the little brother also needs that so I should give them money.
Now, taking a step back. This family has gotten treatment from me MANY times. Several times, when I've tested and gotten a positive for malaria. So treated them.  They also have heard my tirade spiel many times about partial/ under treatment for malaria making it worse.  And how malaria never gets better in one day.  And about how bad it is to treat for malaria without a positive test. And about how malaria has fever, and body aches, and vomiting and headache all together, not usually just one of those symptoms and not just for a few hours.
So, why, after they called me and I came, do they just do what they want anyway?  I know they are ridiculously poor and don't have money to just throw way. And I think I have proven myself trustworthy in the past.
And possibly, if this was one family or an isolated incident I wouldn't even be writing about it. Yet, I have been teaching this same thing about malaria and treatment and the importance of a positive test and the actual symptoms for a while now. Why does NO ONE believe me?!