The Law and Prophets did not end at the cross, nor did the old covenant end at the cross.
The writer of Hebrews said the following about the OC many years after the cross:
(Heb 8:13) By calling this covenant “new,” he has made the first one obsolete; and what is obsolete and outdated will soon disappear.
As we see above, the OC was obsolete, but hadn't completely disappeared yet as of the time Hebrews was written.
Hebrews was written shortly before 70AD. Just like the writer of Hebrews said, the OC soon disappeared for good in 70AD.
We now live fully in the NC.