Is blood discharged twelve days after purification, which has the characteristics of menstrual blood and continued for four days, considered menstruation or a result of contraceptive use?

This blood is not considered new menses due to the short duration between it and the cessation of the previous blood, nor is it a continuation of the previous menses due to exceeding the maximum duration of menses (fifteen days). This blood is istihadah (non-menstrual vaginal bleeding), and your ruling is that of a woman experiencing istihadah.