2004 Buick Rendezvous transmission fluid leak after flush

Hi, My Rendezvous didn't have any leaks whatsover till I took it to my local garage and had the transmission fluid changed. Now there are pink spots under the front. Took it back to the garage and when they looked, they found the lower line leaking. I asked if this was due to the flush they did and they said `No'. I am suspicious to say the least at the coincidence. Should I go after a free repair bill this time? I'm not really much of a mechanic. Appreciate any input.