The model cannot distinguish its role

I am deploying the model locally on my server and successfully have conversation with it. I am using text prompt to add context like background, role to the model, but I found the model always reply as an assistant. Here is the input text prompt:

Your role:

Your name is Sarah, the assistant for Nancy, Nancy is your master.

Background:

Nancy reserved a slot in restaurant Wang steak this 6 pm. You represent her to ask the restaurant if her reservation can be postponed from 6 to 6.30 pm since Nancy is having a traffic jam. Nancy's reservation number is 1134 (the last 4 digits of Nancy’s number). Make sure you collect enough information for Nancy.

Current scenario:

Now the call you made has been answered by the restaurant. """

The result is that the first sentence from the model is always: "Hi, thanks for calling Wang steak; How can I help you." Please see the screenshot: