Something similar happened to us. We had used a secure parking place in Edinburgh, while we went for a holiday to Tenerife last year.
The car park itself didn't look very secure (I think it was new and still being developed). Although it did have an alsatian on patrol, which came up to me to be petted and fed with my sandwiches.
We left the car and went on holiday. On return, the bus dropped us off and we went straight to the car, because the keys were in it. Apparently the keys were in it for the whole week since we dropped it off. They had locked them in it. They were hoping we would have a spare set ( I usually do, but, sods law, this time I didn't). They proceeded (3 men) to stick bits of metal through the top of the window to try and lift the latch, but it didn't work. Then they started yanking at the door and tried to pull the window down. When that didn't work, they started trying to lift the rubber seal round the windows, then they told us the best thing would be for us to BREAK the window (this way, they wouldn't be to blame for the damage!). I asked them if I could call the police, as time was getting on and we had to get back down to Ayr. When I did call the police and explained what had happened, the police said, thjey couldn't help, but don't let them damage your car, it is up to them to get you home safely and get the car back for you. In the end, they got one of their men to give us a lift home, when we got home, we gave him the spare set of keys and off he went. He returned our car to us the next morning. When I told my husband that I wanted to take this further, because there was damage to the car at the seals and round the door and also paint chipped where they were using the wire to gain entry, he said he didn't think it was worth the hassle. So, I think they got off lightly. I will never use that company again. I can't even remember their name (maybe just as well!)