For future reference:

If I were you, I'd book Avianca. They're Star Alliance, and you can credit miles to United - you'd be earning both RDM and PQM.

When calling Avianca, if you have a Spanish-speaking person in your party, their line in Spanish seems to be better staffed. During their pilot strike, I was able to reach out to their Spanish line faster than their English line.

Good luck on changing your flights. Fortunately, you've got some time until your flights, but I'd still take care of it as soon as possible to have a bit more options.