Why have I slowed down?

Last month I started a new telemarketing job in corporate IT sales. I sell perimeter security solutions (firewalls mainly).

In November I generated 8 appointments and closed a 10k and 25k deal. I was the top salesperson in my office. My new boss sang my praises "I hope you were all listening to that call dreamer123 made. That's how you book an appointment"

It's Decemember now and I can't get through to anyone no matter how hard I try. Why do you think this is happening? Is it my mental state do you think? The guys who I do manage to get through to are not intrested at all.

The one objection which is becoming more and more frequent is "because it's a matter of IT security we don't disclose information over the phone because you might be a hacker" any good ways I can deal with this?

In every sales job I have had the first month is usally great but then it all goes pear shaped. Why is this? I have also noticed that whenever I used to get a bit of a telling off for not performing to expectations 90% of the time I would walk out of my managers office and close a deal within the hour. Why does this happen?

Thanks ever so much!