I had similar issues getting CloudMQTT to 'talk' to Node-RED and a Wemos D1 Mini (ESP8266).
I eventually gave up and found another provider... BeeBotte
They offer 'free pricing plans' (with usage restrictions) - which means you can experiment with it in your projects.
Really sorry if this suggestion drags you off in another direction - but I think you might have more success and I think quite a few people on this forum use it (including me) so could offer help.
PS:
Here's a link to a tutorial, from one of my IoT students, showing how he used BeeBotte in his Weather Station project.
http://resources-area.co.uk/bohunt-projects/weather-station/stage_4.pdf
