Laravel 4.2 Website Changes

General information for the website: Booking website for disco and children's entertainer
Description of requirements/features: I have two websites that run from the same Laravel 4.2 booking system, my previous freelancer made some changes to the website that were not completed correctly and now has no time to fix them.

This project is to fix the following issue.

Step 1
Customers visit my booking form at http://www.coolkidsparty.com/?p=35.
They choose a date and venue postcode

Step 2
They choose a timeslot

Step 3
They input their details

Step 4
They are asked to pay a deposit of £10.

Step 5
They are transferred to Worldpay to pay the £10

Step 6
The customer submits their payment details on Worldpay.

This is where everything starts to go wrong!

The customer isn't presented with a confirmation message to say their booking is saved
The admin website where I manage the bookings at https://www.discos.uk/admin states that the customer paid a £30 deposit when they only paid £10
The customer receives an email from my website stating they paid £30
Extra notes: