end contract for contractual employee

Dear Atty.,
meron po kme employee first contract nya is 5mos.. suppose to be iregular na nmin cya kaso nd nman masyado maganda ung performance nya.. kya inextend ang contract for 3mos. as probationary... ung sahod nman nya is below minimum wage pero bago cya nagsign ng contract alam nya lahat kng ano lng ung mkukuha nya sa company hindi rin kasi kalakihan itong company namin. now nung na finish contract na nanghhinge cya ng back pay, tinatanong namin siya kung anong backpay ang hininge niya pero ang sagot lang niya samin basta backpay ng contractual employee.. nakukulitan na rin kasi kami sa kanya kaya na advise namin siya na magcomplain nalang sa labor. ano po ba gawin namin in case na mag compalin talaga siya.
thank you.

get a lawyer because i would consider him a regular employee and payment of less than minimum is unlawful

eventhough he has agree for the salary?
thank you.

eventhough he sign contract and agree for the salary?
thank you.