There is no col-??-offset-0. All "rows" assume there is no offset unless it has been specified. I think you are wanting 3 rows on a small screen and 1 row on a medium screen.
To get the result I believe you are looking for try this:
<div class="container">
<div class="row">
<div class="col-sm-4 col-md-12">
<p>On small screen there are 3 rows, and on a medium screen 1 row</p>
</div>
<div class="col-sm-4 col-md-12">
<p>On small screen there are 3 rows, and on a medium screen 1 row</p>
</div>
<div class="col-sm-4 col-md-12">
<p>On small screen there are 3 rows, and on a medium screen 1 row</p>
</div>
</div>
</div>
Keep in mind you will only see a difference on a small tablet with what you described. Medium, large, and extra small screens the columns are spanning 12.
Hope this helps.