2003 Jeep Liberty overfilled with oil

Engine Mechanical problem
2003 Jeep Liberty 6 cyl Four Wheel Drive Automatic

took my 2003 jeep liberty limited edition in to have oil change, on the way home started to sound rough so next day we took it for diagnostics at the parts store said spark plugs 3 and 5 were fowling so we changed them all, took it back the next day checked it again still the sme thing so we changed 2 core packs still no good then my husband decided to check the oil and found that it was overfilled. Called the oil shop and they sent someone out to take some oil out and found that it had gas in it. He said that the manager would call us back but he did not so I called him. He says that the oil change did not hurt my car but it was fine when we took it in and now it want crank. We asked him to change the oil again for free and he refused so we changed it ourselves to no availe still want crank can any body give me any advice