PHP + MySQL Interval query last 1 month with sum problem

Question

My aim is to sum the MBSENT and MBREC values from the last 1 month for every user.

This is the log (what i want to sum later):

USER  MBSENT MBREC  TRUSTEDIP   REMOTEIP        DATE            ID
csib    99  0   x.x.x.x.x   10.8.0.6    2015-03-04 12:19:14 3
csib    30  0   x.x.x.x.x   10.8.0.6    2015-03-04 12:22:02 4
kwai77  10  0   x.x.x.x.x   10.8.0.10   2015-03-04 12:23:22 5
kwai77  24  0   x.x.x.x.x   10.8.0.10   2015-03-04 12:28:18 6
kwai77  2   0   x.x.x.x.x   10.8.0.10   2015-03-04 13:15:29 7
csib    10  0   x.x.x.x.x   10.8.0.6    2015-03-04 14:32:01 8

This is my code:

$sql = "SELECT SUM(mbsent) AS summ FROM data WHERE datum < DATE_ADD(NOW(), INTERVAL -1 MONTH) AND user='csib'";
$result = $conn->query($sql);
if ($result->num_rows > 0) {
    echo "<table><tr><th>MBSENT</th><th>user</th></tr>";
    // output data of each row
    while($row = $result->fetch_assoc()) {
        echo "<tr><td>".$row["mbsent"]."</td><td>".$row["summ"]." </td></tr>";
    }
    echo "</table>";
} else {
    echo "0 results";
}

This is my code but not working, somehow as i see it is always returns with the first mbsent value. Not the SUM of the MBSENT value with user csib.