Combo SelectOption - Variable 0

I have an HTML page with some tables. these tables contain a ComboSelect and in the last table an input text to fill in a date. When I select comboselect and commit the date and sub-page, comboselect data is not saved correctly in the database, just by adding the "0". In apache the error indicates that the select combo variable has not been defined / fed:

Undefined index: selectteste

Form

           <td>
             </a>
               &nbsp&nbsp&nbsp&nbsp&nbsp&nbsp<a class="btn btn-danger" href="xxx.php?id=<?php echo $fetch['id']?>" aria-label="Settings">

              </a>

         </td>
   <form action="xxx.php?id=<?php echo $fetch['id']?>" method=post>
   <td><select name="selectteste" class="form-control"><meta charset="UTF-8">
   <option value="Teste">Teste Form</option>

</select>





<!-- Text input-->
<!--<form action="xxx.php?id=<?php echo $fetch['id']?>" method=post>-->

<td>

  <input  name="protocolo" type="text" placeholder="00/00/0000" style="width:100px;font-size: 13px" class="form-control protocolo input-md">
 <br>

  <input id="btn" type="submit"  class="btn btn-primary" value="OK" />

  </td>
</div>

Post.php - Post

$selectcombo = $_POST['selectteste'];

The only difference these tables have is within a While, as there is other information to show. I already played the start of <form> at the top of the page and nothing, but I have no idea how to solve it.