Did not get 30 days car rental as per agreement

My vehicle went in for repairs and i received a rental vehicle from Avis. I was assured that i had 30 day car rental. I even received an sms stating that the vehicle only has to be back on the 26th of December 2017. My car went in for repairs. I got the rental vehicle on the 27th of November 2017. I returned it on the 19th of December 2017. When Avis repayed my deposit it was not for the full amount of R1350. Avis charged me for an additional day. They said that discovery only authorised 22 days? What am i missing here as i have it on my discovery insure that i am eligible for 30 days car rental? Please assist. Avis reference numbers: E ********** 85 & ********** 8ZA1. Discovery Reference number: **********