Observation Details
The tariff cards in section "Young-Smartphone-Tarife" are labeled "Slide X von 4", providing no information about the card's contents. The content itself then starts with "S", "40", "GB", "+ 20 GB mit Young-Streaming-Vorteil".
The actual tariff name is not stated in the section at all.
Remediation Notes
Using the HTML article element for the cards is recommended. As it already uses the article element, the surrounding <div> can be removed or stripped of its ARIA attributes.
The card's first content element should be a heading that describes the card's content in total. This can be the tariff name for a low effort solution.
Ideally, this will be the tariff name or a combination of the most important information, like tariff name, GB count, and maybe even price, all of which should be done by existing content:
<article aria-labelledby="s-heading s-data s-price-offer">
<h3 id="s-heading">MagentaMobil S</h3>
<p id="s-data">40 <abbr title="Gigabyte">GB</abbr></p>
<p>+ 20 GB mit Young-Streaming-Vorteil</p>
...
<dl>
<!-- Price information -->
<dt>Ursprünglicher Preis</dt>
<dd>statt <s>29,95 €</s> <abbr title="monatlich">mtl.</abbr></dd>
<dt>Angebotspreis</dt>
<dd id="s-price-offer">19,95 € <abbr title="monatlich">mtl.</abbr></dd>
</dl>
...
</articleThis way, a user of assistive technology will get announced "MagentaMobil S. 40 Gigabyte. 19,95 € monatlich." when the article receives focus. The user than may navigate between articles in the section without moving into or through each card but still getting the most relevant data.