DESING A FREE TO TRY PLAN, This is what I did

1. Create a FREEPLAN with PRICE 0 and 1 month duration

2. Suscribe A New Client with this FREEPLAN it works Ok

When I use the product URL to suscribe the client to a NON FREE PLAN, the system show an error told me 

the Company is already Added and I cannot continue.

The effect I want to get is to Offer a FREE TRIAL without getting credit card Information

Any comments to achieve this ?