I would email
the head of finance
the head of HR
the head of data protection
[ ^ this way its a multi-department problem that at least 1 manager will want to make sure is resolved by themselves or other department head]
Title the email
Payroll advance authorisation requested due to payroll error.
And opening paragraph
that you are requesting to have an advance of £xxx on your wages equal to the money that you are loosing from the UC CT support paid into your account.
[ this ^ is to show that you are willing to work with them to solve the problem and are not looking for "free money" but expect to get money to live on this month]
This is due to ongoing payroll errors which has left you with less money / without money to pay for food or rent this pay period..
That you would apreciate an urgent response to this as you have no savings or access to any other funds.
Next paragraph
List the details of what you are aware of
Not due any wage this month
Your HMRC file had the following data
wage / tax / Ni
uploaded on ...
No payment processed to your bank account.
next paragraph
what UC / CT . Should be due £ xx from... £ xx from...
[ if you dont know the exact amounts use estimates]
what you will now be paid
And the difference [which should be the same as the amount in the first paragraph]
Add in other paragraphs about the Prior errors.
[Dont ask for these to be "solved" or give any detail other than the payroll data sent to HMRC]
If you incurred bank charges or other cost/fees I would add these in.
Second last paragraph
That the errors have cause significant financial problems and once again this month you are left unble to cover your bills and rent which is likely damage your credit rating and leaving you at risk of being left homeless.
Closing paragraph
You trust that they can resolve the issue but if not can they advice you who you need to contact to resolve it.
asking them
to contact you if the need details and supply a personal moblie for direct contact.
to make the payment to your bank account which is on file or you can supply it directly to the people organising the payment.
Keep the email blund and as easy to read as possible. Dont go into massive detail on who said what etc as you aim is to get the advance money approved and/or the managers to decide for themselves to instruct the payroll department to make the changes.
I would inform your manager but not include them on the mail and forward the sent email as an FYI.