My data not supp**** as promised

I upgraded my contract on the 24th November 2017 and I was told I will receive a 30GB split equally in three months, I received my first 10GB on the same day and the second one on the 22nd December and now on the 22 January 2018 my last 10GB hasn't been loaded with my monthly subscription. I would like to get an explanation on this and my account is credited with 10GB as promised.