Feeling this is going to be unpopular.
Sending a player off for calling a CAR a "cheat" is a massive overreach.
Let’s be realistic, Club ARs often lack the fitness, concentration, or neutrality required for the role, often guessing in favour of their own team.
We’ve all seen the YouTube clips of managers screaming "get the flag up" while a distracted teenager blindly obeys. Whilst a player who might have started their run, 10-15 yards onside sees their goal chopped off.
Use the step approach, like any other player to player interaction.
Shield your CAR and show them the respect they deserve for taking on this role, by blowing on dissent early, deliberately to drown it out and draw the heat toward yourself. You are the match official not the CAR, it is your decision. So if your CAR flags offside, and you agree. That is your decision, let the players know it and move on.
If you’re dismissing players for a trumped up 'calling a match official into disrepute' charge, when they vent an obvious frustration, you’ve lost touch with the game. In fact, some biased CARs love the victory of getting a player sent off.