Phathetic servic, ***** .

Very pathetic service .i bought a an m5 from zido cars .as i was driving home d car gave me problems .den i took d car back 2 days after n insisted on a refund n they told me the cant do it n i must take a car or 2 to cover d cost so i took 1 car n i asked for the balance to b refunded n they said no i must take another car n den they told me abot a chev utility any they over charged me .now im not happy n want my money back.the even blocked my number .how do i go about doing this?