about to store multiple values of child checkbox related to parent checkbox, data is store only one time

when i store services and activity then services and activity value store multiple times in database, i also use implode instead of foreach but that time first service and first activity stored,the following image describe idea about what i exactly want

<form method='post' id='userform' action='savecheckbox.php'> <tr>
<td>Trouble Type</td>
<br>
<td>
 <input type='checkbox' name='servicevar[]' value='1'>tds<br>    <br>

<input type='checkbox' name='activityvar[]' value='1'>Return<br>
<input type='checkbox' name='activityvar[]' value='2'>Filling<br>
<br>


 <input type='checkbox' name='servicevar[]' value='2'>Gst<br>    <br>
<td>

<input type='checkbox' name='activityvar[]' value='1'>Return<br>
<input type='checkbox' name='activityvar[]' value='2'>Filling<br>
<br>

<input type='checkbox' name='servicevar[]' value='3'>vat<br>    <br>
<td>

<input type='checkbox' name='activityvar[]' value='1'>Return<br>
<input type='checkbox' name='activityvar[]' value='2'>Filling<br>
<br>
</td> </tr> </table> <input type='submit' name="submit" class='buttons'> 

<?php 
if(isset($_POST['submit']))
{
$activity = $_POST['activityvar']; 
$service = $_POST['servicevar'];


foreach ($service as $key => $servicevalue) {
    foreach($activity as $key=>$activityvalue)
    {
        $query = "insert into serviceacitivitymap(service_id,activity_id)values('$servicevalue','$activityvalue')";
        $insert_row=$conn->query($query) or die ($conn->error.__LINE__);

    }



}

}

?>

• recent output image

• expected output image