What are the consequences for someone who intentionally broke their fast in Ramadan for many years before becoming religiously committed, and how can they atone for that and escape Allah's punishment?

It is obligatory upon you to repent sincerely to Allah, the Almighty, and to regret what has occurred in terms of shortcomings and negligence. Among the conditions for your repentance is to make up all the days you missed fasting from the time you reached puberty until Allah bestowed repentance upon you. You should make them up according to your ability and capacity. Expiation is only obligatory for breaking the fast by intercourse. Strive in seeking forgiveness and increasing in acts of obedience and supererogatory worship.