How do I handle players that don’t care for the rules I put in place as the DM and question everything I do?

I am DMing a game of dnd 5e or close to it. It’s a homebrew campaign. We are mostly new to D&D with the exception of 2 players that play with other groups.

I have 2 players that seem to question everything I do as a DM and make the game hard to DM. One of the things they question is cantrips.

I had one of my players call my ruling stupid and log out. To put it into context I make my players roll to see if they can land the cantrip. 2 of my players have recently questioned why they have to roll at all and why it just doesn’t do what they believe it should do. But there is nothing in the rules about rolling and cantrips.

It was a cantrip called "mend" and he was trying to use it to repair his armor which had been broken. I made him roll to see how well he repaired it and he got a 2 so it didn’t repair much. He went behind my back and spoke to another player about how it was stupid and "that’s not how cantrips work" even though he was able to cast the spell, just not well.

I don’t want to just put my foot down and say "I’m the DM, what I say goes" but they won’t listen to my reasoning and just keep saying I’m wrong. How do I handle this situation? It’s getting to the point where I am considering stopping DMing all together.