Strictly speaking Michael at some time you should have received a Housing Benefit letter showing the calculated assessment.
On that calculation under 'Applicable Amount' it would show either Single or Couple.
I'm guessing that your local council might be able to send it to you from the archive....maybe worth asking.
If you got paid too much it's most likely their error as I'm sure you informed them of the immigration status of Maritess. Still might need to pay back any overpayment though.