Carers allowance not paid this month?

My wife is a full time carer for our severely disabled son, she has claimed CA for about 4 years now without a hitch, the last payments we had were on 7th Jan, then 4th Feb, then 4th March and another on 28th March, any idea when we can expect the next as its supposed to be 4 weekly, we got the DWP letter today saying the rate has gone up so there isn't any issues I think.

Any help appreciated form anyone in the same boat.