Lcwra Backpay

I put in my first sicknote on feb first and got approved for lcwra group a few weeks ago. Because my claim period is the 10th to the 10th I got my first higher universal credit award on the 16th but there are 9 days between when the three months waiting period ended on May 1 and the first full claim period. When I asked about when I will get paid for those nine days I was told the following: "Hello, I am sorry I think there has been a bit of confusion. There is no 9 days due the system will not issue arrears for 9 days it will only calculate payments for a full one month period and that is what is included in this payment.” Is this correct? It really doesn't seem fair