Contract law - Does a precedent overrule the terms and conditions of a contract?

[ryscford]

A breakdown service have fixed the same vehicle for me (my only vehicle) six times in the last four years. I rang them today and they say the vehicle is 18cm too long to be covered under the terms and conditions of my cover. It is personal cover rather than vehicle cover.
My question is, given that I renew my cover each year based on the fact that they have fixed the vehicle in the past, does that constitute a precedent that obliges them to attend to that vehicle regardless of the terms and conditions?
Many thanks for your time if you have read this.