Yes. Consider implementing more of the self-referral process. In this process you learned to discover things that are Meaningful, Important, Significant, and Compelling about your friend, family member, colleague or acquaintance. This relevant information helps them understand why scheduling an appointment with you is in their best interest.
The other thing to consider is that you should not have to work very hard or sell existing clients on coming to see you for any reason. Why do they think calling you back is optional? You’re their Financial Advisor. I would think they would call you right back whenever you call for any reason. For those people who don’t call you back you can consider a sign from God they definitely are not and will not ever be Ideal Clients.
On the other hand, if you really want to send a wake-up call to get them into your office and shift the relationship from something they consider optional to a more serious point of view, consider something like, “in order for us to determine if it makes sense for you to continue to be our client, we need to meet with you and your spouse at our office as soon as possible. Call me back right away to schedule your appointment. If I don’t hear from you within 5 days I’ll assume that means that you no longer wish for me to be your Financial Advisor and I’ll send you the necessary paperwork to transfer everything to someone else.