For free? I'd have expected a small charge for their time. Perhaps they have closed their service department?
Should be easy to measure the accuracy if you get a 1 meter lever and some known weights to hang on it. I made a thread about this a while ago as the units were confusing me, I needed 2Nm which is right at the low end of my small uncalibrated wrench.
Free calibration is a bad business plan... Most torque wrenches last decades if looked after - especially the type of people who need a yearly calibration!