1999 Dodge Neon Tune up gone wrong

Engine Mechanical problem
1999 Dodge Neon 4 cyl Two Wheel Drive Automatic 76.000 miles

I got my neon last year, and it was running great. I thought it was about time for a tune up because it was starting to run a little rough and was using more gas than it did when I got it. I then replaced the air filter and was changing the spark plugs when on the 3 plug when the plug wire didn't want to come out, after pulling hard it came off and it was torn, the rubber was melted on the plug, wasn't able to replace it. I then put the old plugs in again, but afterwards the car has run extremely rough and badly, I went to a garage and had them remove the plug and put the new plugs in but it's still doing the same. They said their was oil leaking by the plugs and it needed replacing something that I can't remember. I'm hopelessly lost. I just don't understand why it's running so much worse than it did before Will new plug wire fix the problem or is it a bigger issue?