Slp/appeal- mat suit

An application u/o 9 R 13 was allowed in lower court and the ex-parte decree was set aside. Approached high court against the order but it was not allowed. Both the courts overlooked a key factor in service of summon which was later discovered by us from case record in lower court but it was not heard at all and a order was passed by High court. I want to approach Supreme court as I feel gross mistake was made by both courts. How should I proceed now?