Bad after service

took my vehicle to Loop Street office for a service with no miss on the idling, I left to go down the road after the service and the first stop the car wasn't idling properly. I came back immediately to have them assess, the mechanic took a look and said it was the throttle body that needs to cleaned and they wanted to charge an additional R550 to clean it. I left because of time and took it to another mechanic to find out the spark plugs that i paid an additional R380 was not put through a feeler gauge and the gaping was wrong. i called back and Eve who i spoke to said they cant assist because i went to another mechanic. the only reason i did that is because the mechanic that checked out the car was hell bound that it was the throttle body. I paid an additional R400 to let me know the place that did the service did not do its due diligence by checking the fault... i was told they cannot do anything. i know the price of the service was less but dont just try and make more money by looking for unnecessary item to change. the spark plugs costs R180 for 4 at Suburban spares and they charged R380 for it