I think the problem is that the wording on our accounts does imply that the money will land in your account each month on the day you sign up. Not a few days later.
Account interest payments
Interest is calculated daily, and applied to your account monthly on the date your account was opened. So if you opened your account on 27 September, your interest will be paid on the 27th of each month. When that date falls on a weekend or bank holiday, the interest will be credited by the end of the next business day.