What are the practical steps to deal with the repeated refusal of the girl's family to allow marriage, due to the suitor being from another city, despite mutual feelings and compatibility between the two parties, and given that you previously advised the suitor to cut off communication and return after graduation, which he did?

Marriage is better for those who are in love. Differences in cities, customs, or age proximity are not religiously prohibitive. Continue trying to convince the family, seeking Allah's help. If it becomes easy, then praise be to Allah. Otherwise, separate, and may Allah enrich each of you from His bounty. Entrust your affair to Allah, and do not pay attention to thoughts of blame.