Yealink t55 skype config

Hi All.

I hope someone can assist.  A client has bought T55's for use with Skype but their calendars are apparently 1 day behind.  the phones have had the latest firmware installed and all config seems ok. Calls are flowing without issue.  Does anyone have any experience with these devices or can anyone make any suggestions that may have an effect in this instance.  NTP has been checked on the device GUI.