I've had that happen with other MSC's before. If you had the negotiated price in writing (i.e. email), you could feel comfortable doing the shop immediately while waiting for it to be resolved. However, as it was just a verbal agreement, I would not perform the visit until the issue is rectified. Be sure to notify the scheduler of your intent to not do the shop until the compensation is corrected in writing, so that s/he knows that there is some urgency to seeing it done.
Hard work builds character and homework is good for your soul.