The first thing I'd say is that nobody buys value propositions.
Really.
Value propositions are useful marketing tools, and useless sales tools.
In phone prospecting you have (approximately) 3 seconds to get 30 seconds to get 3 minutes to get 30 minutes.

If you don't sound right, you will have a challenge getting 3 seconds and rarely 30 seconds.

Your question is not actually about Value Proposition as much as it is about Prospecting.

This might be fixable...

Cheers,
Marty