I had several issues with refurbished lenses from Canon. One was a 15 2.8 Fisheye. The aperture stopped working in hot humid conditions. I had to send it back twice until it was fixed. Had to pay shipping from my side, but in the end it was worth it and the lens now works flawlessly. I also bought a 24-70 2.8L (Mark I) which arrived with a boatload of what seemed like lint not behind the first, but a element further in. This was cleaned perfectly the first time around.
Both times I also told them to adjust the focusing, just for the heck of it, I figured if they slacked originally, this would make sure they check it. I have to say, both lenses are very sharp now.
Long story short, send it back, you did pay enough money to expect a clean front element in my opinion. I wouldn't mnd an exterior blemish on the lens if it's refurbished, but the glass should be clean and it should work flawlessly.