Is it permissible to use an internet card, purchased with the intention of committing a sin and then its owner repented, for studying?

Using an internet card for studying and for permissible, beneficial matters is halal (lawful). The fact that it was bought for a haram (unlawful) purpose does not make its use for halal matters haram. The important thing is to remain steadfast in repentance, beware of the whispers of Satan, and seize time with righteous deeds.