Hi Yesuf
DWP were probably carrying out due diligence, I would not worry where payments come from as long as you receive payments for the correct amount.
I could be the previous residents had not let DWP they had moved, as we all know moving home can be very stressful and things easily forgotten such as notifying DWP change of address or notifying Royal mail. of a change of address to get your post redirected.
Gary
Nothing on this board constitutes legal advice - always consult a professional about specific problems