no couriering of registration certificate

I have paid off my vehicle finance through Nissan Finance. I now wish to sell my vehicle but need the registration certificate. I contacted them 13 July 2015. I was promised that they would courier the documents within 4 to 5 days. I phoned Thursday to find out what was happening and was told that the documents had been couriered and I should be receiving them that day, 16 July 2015. No arrival. I phoned Friday to be told the same story. No arrival. I phoned Monday 20 July 2015. Same story. No arrival.<br> <br> I have run out of patience. In any case, should these vehicle financing people not give the registration certificate to the vehicle owner as soon as the vehicle is paid off? Holding on to a registration certificate that no longer belongs to you seems like theft? Why must I beg for a certificate that now rightfully belongs to me?