Brake lights will not turn off

Hello,

For the past few months I have been encountering problems with my car. The main problem is that sometimes (maybe once a month) when parking up somewhere, all of a sudden my brake lights won't turn off even though the ignition is off and the key is not in the car. Then when I try to put the key in and start the car, it won't start, but the brake lights turn off. As soon as I remove the key, the brake lights are back on. I then have to let the car battery die and jump start it to get it back up and running again. I've taken it to two mechanics and paid so much to get this fixed, but nothing seems to fix it. To note, I do have an oil leak, but I don't know if this is effecting it. I also have an engine warning light on my dashboard. I have taken all these issues to mechanics to fix and even after being promised its fixed, it doesn't appear to be. I don't know what could be causing it and I've searched high and low for an answer.