هل يجب قضاء صيام رمضان الماضي بعد التوبة من ترك الصلاة بسبب الوسواس القهري؟

You must take the initiative to make up the Ramadan days before the next Ramadan arrives. It is not permissible to delay making up missed fasts until after the following Ramadan, unless there is a valid excuse. If you have already made up the days you missed, you are not required to make them up again after repenting from abandoning prayer. Rather, you are only required to make up those prayers.