Apparently it's because parted only shrunk your partition but not the ext4 filesystem on it. Unlike gparted, parted no longer does anything with the filesystem layer. So you need to shrunk the ext4 with resize2fs first.
made a new one in its space
If you only created a partition (but not formatted it with any mkfs.*
yet), you can probably delete the new partition, and extend the shrunk partition again. If it mounts again correctly, then you can shrink it again with the aforementioned proper procedures. You may also want to run fsck first before you mount it.
However, if the new partition has been formatted already, there is almost certainly data lost. For that you may need a more "professional" approach to rescue it.