Do I need a firewall to protect my IP address?

Hello. 

This morning I called the Technical Support Number available thru Norton (1800) 616 560. (Rising Solutions) The technician accessed my Laptop and after a test which I did not ask for, he told me that I had a Network Security problem and urged me to buy a  Network Security Firewall program which costs $300 dlls! He told me that my network was compromised by a trojan horse which is stopping Norton 360 from working correctly and that there was nothing I could do, but buy the Network Security Firewall program.  Is this true? It sure seems to be a scam.  Is my laptop and all the devises I have connected to that network in danger of crashing? 

 

Can someone help me?

Thank you so much

Norma