The old adage that you can attract more flies with honey than vinegar seems pretty quaint in this day and age.
Yet there are some sales people who need to be reminded of this principal.
It seems to me that if someone is giving you less business than usual you have only a few choices on how to proceed.
Assume they are a lost customer and take them off of your mailing list
Assume that there is a problem and ignore it
Assume that they are now in a relationship with your competitor and get mad about it
Or, and I know this next one is a little crazy,
Ask them to lunch.
Ask them what has changed with their business.
Ask them what they need that you aren't providing.
Mostly, just ask.
Why would you assume and then react?
If you want to know why you are no longer getting business from them, ask them. Find out why. You might be really surprised about what you hear.
But, I can guarantee you that you will never know if you don't ask.