2006 Citroen C4 too much oil

Hi all.
Firstly I know very little about cars aside from how to drive one and basic bits of maintenance.
Recently we had the car serviced. About 3 mth later the car showed a low oil warning.
Now the dipstick in our c4 seems to go around bends and up and down hills before locking into place!
Mechanics have commented on it in the past and said it does make it very awkward to check.
Anyway, it was checked on as flat an area as possible at the time, about 5 times with 5 different readings!
As the car had given a low oil warning we added more oil and all was good. Every few weeks then low oil warning came on so it was topped up a little. Anyway, the wife started it to come home from work this week and once again, low oil. This had never been an issue before so we just assumed that on the service they had only filled it to minimum and we were just having to pop a pint in every few weeks. For the first time ever the car was parked facing up on a large hill. Next morning I went out to use the car and it turned over but didn't start. Tried again, turned over again still wouldn't start but no low oil warnings. Phoned RAC who basically turned up, tried starting it a couple of times until it got to just a click on turning the ignition. Said it needed to go to a garage, offered to tow me but I had to go somewhere so left me with the car and the advice of "remove the spark plugs to let any pressure out, remove some of the oil until its at correct level, leave it for a bit, put it all back and start it.....then buy a new dipstick!" Sound advice if I knew what the hell I was doing. It is my wife's car. Mines a ford focus. I can actually see where the plugs are on mine!! Any advice would be much appreciated before we take it to a garage who can tell we know nothing about cars and just hit us with a bill that resembles a bloody phone number!
Thanks in advance!
Steve