Regarding the follow-up comment above... any mechanic or service manager who tries to tell you "too much oil can't damage an engine" is trying to pull a fast one. Too high an oil level causes overpressure that can lead to all kinds of havoc such as blown or damaged oil seals just for starters, to say nothing of the other issues mentioned by others like the excessive level meeting the bottom of the crankshaft and so being "whipped up" (or just as likely causing extra drag and friction right where it's never intended to be, and maybe bearing contamination/extra wear), excess flooding of the pump, passing through of oil to the exhaust system (catalysers get very hot, and don't like being contaminated).
There's a reason dipsticks have "maximum" marks on them as well as "minimum"... you don't just put oil in until it reaches the minimum mark, then dump in whatever you happen to have left and hope for the best. "Accidentally" putting in the oil twice should be something you can't miss, if you're actually checking the level during and after filling, to make sure that it's not only over the minimum (you need to make sure of THAT!), but no higher than the maximum.
I don't think I've yet had a vehicle where the manufacturer recommended oil fill volume actually matched how much was needed to reach the maximum mark... it's always been a little less. After seeing it over-fill a bit the first time I did it, running to the recommendation, I've always stopped at least a pint / half litre short, let it settle for a minute (or 2~3 in autumn/early spring, 5 in winter), checked the level, and topped up accordingly (there's usually about that much between the minimum and maximum, so you can make a reasonable guess about how much of the remainder to put in). If what they're doing each time is dumping out the old stuff and then refilling with the exact manual-recommended amount, without accounting for how there will always been quite a bit of the old oil still lurking in different parts of the engine, and NOT checking the dipstick after filling... which is the only way they could possibly have missed a "double" fill... they're likely habitually over-filling every single car that passes through their doors, to a greater or lesser extent.
In short: cowboys. Get whatever reparations you can from them, complain like hell to corporate, and do not, under any circumstances, ever go back there once the situation is straightened out.