Hello Fughuehoo18
A Swiss Half Fare Card cannot be cancelled. It has a fixed validity period of one month, you should not get confused, as you likely used the Half Fare Card for residents, which lasts 1 year.
I suggest that you should see an agent in a station travel office or to call the SBB Contact Center to clarify the issue; here in the SBB Community we are unable to assist you with any questions that involves personal data.
SBB Contact Center: 0848 44 66 88 (CHF 0.08/min, 24/7, waiting times are possible). From abroad: +41 51 225 78 56.
Kind regards,
Roland