the CBS app did this to me. I signed up for a free trial, watched some Star Trek, and then cancelled. it immediately cut off all my access, and I didn't even get the duration of the month to use. The month that I had paid for.
If this was on iOS then this is explicitly in Apple's guidelines not something that CBS mandated. The guidelines say that any remaining time on a free trial must end immediately if canceled early.
So was it a free trial or were you paying for it? Your comment seems contradictory.