I've had a similar problem when I was trying to call the gardener one day. I had emptied my neighborhood before starting, so there weren't any gardener NPCs around. When I called the service a new gardener SHOULD have been created, but it wasn't. Instead, my sim jumped off the phone and still no gardener.
It worked for me when I spawned a new gardener myself (via the NPC & townie maker tree) and called the service after that. Maybe you could try that with your social worker?