Hi Gary
Welcome to the forum, you might want to have a look at the following FAQ which explains where everything is.
Welcome to Benefits and Work .
I am not sure what number you phoned but I have never received a recorded phone message advising the current return by date.
The number you need to phone is the PIP helpline: 0800 121 4433, best time to phone is first thing in the morning, 8.00 am.
Gary