Did you use a proper allen wrench, or a simple 7mm key from a set? I went through 2 allen keys (Twisted round a few times!), then bought a 7mm wrench which worked fine (needed the use of a large ring ended spanner aswel for leverage)
Also, a socket with a hex top, and a strong enough spanner to fit the hex top should do it...(allen wrench goes through the top of the socket). If the 7mm 'hole' is buggered though.....
As said though, local fitters should sort it, but you'll have to drive back with them loose when it comes to putting them back on something...