Samsung S5 Contract -Top up

Good day,<br> <br> I have bought Samsung S5 at East gate mall ' Telkom mobile' few weeks back asked them for a Top up.<br> <br> Yesterday when I tried to load airtime, it couldn't allow me, I called customer service they told me that I don't have that option, when I tried to escalate that with the sales person she told me she explained that they don't have top ups for S5. Is that possible that Samsung S5 don't have option for TOP UP contract???<br> <br> I'm really frustrated and the salesperson don't respond to my emails, not helping out.<br> <br>