Praise be to Allah.
You should repent to Allaah, may He be glorified, for helping your husband to do something sinful and wrong by getting this interest-based credit card. Allaah says (interpretation of the meaning): Help you one another in al-birr and al-taqwa (virtue, righteousness and piety); but do not help one another in sin and transgression [al-Maaidah 5:2]. You should not have helped him to get this card or responded to his demand for your help, even though he insisted, because the Prophet (peace and blessings of Allaah be upon him) said: There is no obedience to any created being if it involves disobedience to Allaah, may He be glorified.(Reported by Imaam Ahmad in Musnad Ali; Saheeh al-Jaami, 7520). And Allaah knows best.