2005 Toyota Avalon Intake hose

Engine Mechanical problem
2005 Toyota Avalon 6 cyl Automatic 78500 miles

I change the oil on my car every 3000 - 5000 miles. I use top grade oil. I recently had my oil changed. I started to hear a funny nose while the car was running. My husband open the hood to see if he could hear where the noise was coming from. Oil was everywhere! He took the car back to the servicing station. They thought they'ed forgotten to tighten something and replaced the oil. The next morning I noticed oil under my car. The servicing station is now claiming that the intake hose to the manifold is depressurized and they don't know why it happened - of course they are saying that they had nothing to do with it. There was nothing wrong with the car prior to them changing the oil. What could have caused this to happen and what is the estimated repair cost?

Thanks.