Martinez Heavy Truck Reair Refusal to complete work promised huntsville, Texas

On nov 19, I took my truck in for a pm. I had some new mud flaps put on and asked them to disconnect a quick disconnect fitting on and air tank and tighten the existing cap.(A 30 second job) They said ok. I picked it up this morning and told the night mechanic the day shift forgot to do this. He said how do I know they said they would do this(basically calling me a liar)and if he did it it would cost me extra.(really. so I should pay twice?) I have been doing business for 12 yrs with them, but this is the last time I spend one dime there and will bad mouth them to everyone I can.Real great customer relations!