Adding existing customers to Billing Module

[Lee@gpk]

Hi All
We have just installed Plesk 10.1 on a new Server 2008 R2 Sp1.
We are currently hosting customers sites on a Plesk 9.5 without the billing module
We can migrate from the 9.5 server to the 10.1 fine but it does not add the customer to the billing module.
For New customers we can add them in the billing module and it does a sync then then are in the plesk panel.

Does anyone know how we can link existing customers into the billing module?

Thanks in advance
Lee