All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
You are not obliged to obey your father about not visiting your cousin; obedience is required only in what is permissible. However, you may visit your cousin without the knowledge of your father so that you would not anger him.
Moreover, visiting your cousin is not an obligation but you are obliged to keep ties with him according to what is reasonable. The Sharee’ah did not specify a particular method or a specific number of times to keep ties with kinship. Rather, this differs according to the difference of circumstances and customs. So, keeping ties with kinship could be achieved by visiting, contacting by phone [or any other means of communication], greeting and every manner that is considered according to social customs as keeping ties with kinship.
Allaah Knows best.