Players want to make modern Tech in Medieval Times what do I do?

So this is in the home brew campaign that I started when I started with DnD (Yes I started by DMing it was not a good Idea). Now the players are level 8 and they started making electrical motors to make steampunk Airships (which I'm fine with) but recently they started wanting to make propane, cellphones, etc. and its getting really annoying any ideas how to stop them cause they love to annoy me with these ideas.