What area did you find your prints were off the most? Were they too dark or were the colors just off. If too dark, check to see if your monitor is too bright. That can be a killer since it makes your images appear brighter than they really are.
Soft proofing can save a lot of time and trouble if you are having problems with your prints in either being too dark or color issues. I had problems with inaccurate colors when I started with prints a few years back but once I discovered how to soft proof before sending my images to be printed, I very rarely had to send any prints back.
Here is a good tutorial on soft proofing from the company I use for my prints:
I have seen a few people here use their services as well so you might want to try them instead as an alternative to the company you used. If you decide to try another company and don't soft proof you might be stuck with the same results.