Hi, I'm Bomber252525! Will my split UC payments be paid on my regular day?

HHello... I recently switched to fortnightly payments of my U.C. 2 weeks ago I received my new 50% amount of U.C, meaning my next payment should be due tomorrow, exactly 2 weeks after my last payment. Now, I've been told that I must wait until my usual date of payment which would have been the 15th of every month. I've arranged with my landlord to pay my 1st months rent in my new private rented accommodation on the 12th, (tomorrow) as I assumed it would be paid tomorrow as the last payment came 2 weeks ago tomorrow.? I'm panicking now because the payment of £350 is to be taken out of my bank tomorrow, but it's now apparently going to put me overdrawn and my landlord won't be able to take my rent? I'm so confused, I know the 15th only means waiting 1 extra day, bit it's the arrangement myself and the landlord agreed, and it's too late for me to contact them now? I suffer with bi-polar and extremely bad anxiety and this is taking it to the absolute maximum at the moment? Does anyone know? Will my payment be made tomorrow 2 weeks after my last? Or will it not come until the 15th ,which used to be my regular date when I was receiving monthly payments? Furthermore, why didn't anyone explain this to me when I applied to split payments?