Dishonest and false advertising

Dropped off my car for a FREE 26-point Toyota Safety Check as per the sms offer sent on the 20th November. I specified that when I made the booking on the 23rd November and they did a 195,000km service (car was serviced at the same garage end July for 180,000km and the reading is 186,000 odd km). I was told to pay for the service otherwise they will not release my car. How does a car get serviced for a 195,000 km at 186,000? Why didn't they stamp my service book if what they did was right? They held me at ransom for their mistake. They are dishonest and not willing to listen to anyone.