Replace stock level with custom text

I've tried the following code in a views template file like this:

views-view-field--my_view--default--field-stock.html.twig

{% if field_stock %}
  {% set stock = field_stock.0.value %}
  {% if stock >= 10 %}
    <span style="color: green">In stock</span>
  {% elseif stock > 0 and stock < 10 %}
    <span style="color: orange">Limited stock</span>
  {% else %}
    <span style="color: red">Out of stock</span>
  {% endif %}
{% endif %}

but still can't get the view to show the text instead of stock level ....

I've even tried injecting the above code directly as a custom views field rewrite. i can get a message printed but it shows 'out of stock' for all rows even when there is stock. I'm guessing that the issue lies with the field_stock.