Hi vfc. on the assumption that you are new to the site this link should help you find your way around.
Welcome to Benefits and Work I'm afraid that I am rather confused by your post. There are no job centre appointments, group or otherwise, associated with PIP. Are you also in receipt of ESA? If so, in which group have you been placed (or are you still awaiting assessment)? If you are on a joint ESA claim with your wife, this would explain the fact that she has also had a letter regarding looking for work - as she is your carer she would be offered help but not pressurised to look for work.
ATOS are no longer involved in ESA assessments so the letter you received must be related to your PIP claim. If there was no date given you will need to contact them about this.
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