Best Practice: Not Interested? What to say to this response while cold calling

No matter how polished your cold-calling skills may be, you will always get the following responses:  "I'm not interested" or "We're happy with our current vendor."
Expect this and prepare for it.
Resistance after hearing an opening statement from any unknown caller is a natural, conditioned response for many.
These are called Resistant Reflex Responses.
Trying to counter this with logic is often ineffective.  For example:  "What are you not interested in, I have not given you anything to be not interested about yet?"  This seldom if ever works.
What should you do?
Get them talking - this moves them away from their reflexive response.
It is proven that disrupting the pattern is the most effective way around this.
2 Examples:

PROSPECT - "I'm not interested."
SALES PERSON - "I see, who is your current vendor?"

PROSPECT - "We're all set."
SALES PERSON - "Oh? (pause) When was the last time you reviewed your current program?"

Remember - tone of voice plays a key role in this and you should never sound confrontational.  Use a soft, almost surprised sounding tone.