It has been so long since we have had the opportunity to be of service to you, that I have begun to wonder if perhaps, we have offended you in some way in the past.
If this is the case, I would greatly appreciate knowing what happened. In fact, if you have any grievance with our firm, I wish that you would call so that we might discuss the problem.
We have introduced many innovations into our product line since the last order you placed with our firm, and if the reason we haven't heard from you has nothing to do with a complaint, we would appreciate having the opportunity to show you these innovations.
In either case, it would be wonderful to hear from you.