Transaction log Shrinking

Hi

My ldf file has grown to 56gb, I am trying to shrink the ldf file using the below command :

DBCC FREEPROCCACHE
DBCC DROPCLEANBUFFERS
DBCC FREESYSTEMCACHE ('ALL')
DBCC FREESESSIONCACHE
DBCC SHRINKFILE (xxxx_log,1024)

but the file is not shrinking.

The file size increased just yesterday due to some transact operations.

Last night the full backup was taken but still the log file shows this huge size.

Please let me know how can I reduce the file log file size.

Also this database is a Principal server in a Mirror setup, hence this has affected the mirror server as well and the log file has increased there as well.