I need a PA or admin help - someone to chase vat invoices

I have 4 hours or 8 hours worth of PA/admin type work. Essentially it's chasing previous clients via email or the phone to pay the additional VAT we have added to invoices, as we have recently registered as a VAT registered business. Out of the 10 clients, 3 have responded saying they will do/pay and the other 7 need to be chased.

I am looking for someone ideally with some Xero.com, bookkeeping or simply a proactive professional who can communicate effectively via email or phone to get these clients to do us a favour and pay the Vat on the invoices

Please get in touch asap, this is an urgent requirement. Happy to pay a fixed price or hourly rate. The latter probably works better.