Thinking that's the most likely outcome from my POV as well.
After all, if you're pressed into service as a "hacker", it wouldn't take much to discreetly slip information to the authorities, considering that most cartel types don't strike me as being technically uber-literate. Sure it would be a massive risk, but totally doable depending on the environment.
There are enough other hackers under duress willing to snitch on you for trying to send a mayday, plus they are probably operating under the stance of "do what we say and we will kill you, don't do what we say and we will kill your family". On top of that your mayday is likely to end up in the hands of police or military on the narcos payroll.
Part of the Radio Narco objective is to monitor communications of crime fighting orgs. If you did get a mayday sent to the right people, you and the rest of the captives are as good as dead as soon as they start planning the rescue team, and if they do find out it was you who sent the mayday your family is probably going to disappear too. It's a supremely shitty situation all around.