Update Ocomon Connection to PHP7

Question

After upgrading the php version from 5 to 7 the system does not open, the mysql_connect function was discontinued I tried using mysqli and could not make it work.

Error:

Fatal error: Uncaught Error: Call to Undefined Function mysql_connect() in /home/group501/public_html/support/includes/classes/conecta.class.php:53 Stack trace: #0 /home/group501/public_html/support/index.php(44): conexao->conecta('MYSQL') #1 {main} thrown in /home/group501/public_html/support/includes/classes/conecta.class.php on line 53

class.conecta.php

 function conecta($BANCO){
        if (strtoupper($BANCO) =='MYSQL') {

        $this->con=mysql_connect(SQL_SERVER,SQL_USER,SQL_PASSWD)or die(mysql_error());
        $this->db=mysql_select_db(SQL_DB,$this->con);
            if ($this->con == 0){
                $retorno = "ERRO DE CONEXÃO - SERVIDOR!<br>";
            }
            else if ($this->db == 0){
                $retorno = "ERRO DE CONEXÃO - BANCO DE DADOS!<br>";
            } else {
                $retorno = "";
            }

            return  $retorno;

        }

    }

    function desconecta($BANCO){
            mysql_close($this->con);
    }

Then attempt to update

function conecta($BANCO){
    if (strtoupper($BANCO) =='MYSQL') {

    $this->con=mysqli_connect(SQL_SERVER,SQL_USER,SQL_PASSWD)or die(mysql_error());
    $this->db=mysqli_select_db(SQL_DB,$this->con);

        if ($this->con == 0){
            $retorno = "ERRO DE CONEXÃO - SERVIDOR!<br>";
        }
        else if ($this->db == 0){
            $retorno = "ERRO DE CONEXÃO - BANCO DE DADOS!<br>";
        } else {
            $retorno = "";
        }

        return  $retorno;

    }

}

function desconecta($BANCO){
        mysql_close($this->con);
}

**Erro:**

Warning: mysqli_select_db() expects Parameter 1 to be mysqli, string Given in /home/group501/public_html/support/includes/classes/conecta.class.php on line 54

Warning: mysqli_set_charset() expects Parameter 1 to be mysqli, Object Given in /home/group501/public_html/support/includes/classes/conecta.class.php on line 55

Notice: Object of class mysqli could not be converted to int in /home/group501/public_html/support/includes/classes/conecta.class.php on line 56

Fatal error: Uncaught Error: Call to Undefined Function mysql_query() in /home/group501/public_html/support/index.php:51 Stack trace: #0 {main} thrown in /home/group501/public_html/support/index.php on line 51