Greece-Pakistan mixed franking 1968

An interesting mixed franking: Fragment of a cover with a Greek 1961 definitive stamp of 4.50 DR cancelled with a postmark "ΑΘΗΝΑΙ - ΠΑΓΚΡΑΤΙ" on 30 VIII (19)68 and a 90 Paisa stamp of Pakistan cancelled with a postmark dated 10 SEP (19)68. On the back another postmark "ΑΘΗΝΑΙ - ΠΑΓΚΡΑΤΙ" dated 22 IX 68. Most likely the letter was not delivered in Pakistan and it was returned to the sender in Greece with a new stamp.