It is believed that a person becomes pure as a new born baby after performing Hajj so it is compulsory to offer the missed fasting and prayers which were missed before Hajj?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

It is confirmed that the Prophet said: "Whoever performs Hajj (pilgrimage to Makkah) and does not have sexual relations (and all matters that lead to it) with one's spouse and doesn’t commit evil or sins, returns as the day his mother gave birth to him (i.e. without any sins)." [Al-Bukhari and Muslim] Thus, Hajj expiates sins, however, if before Hajj a person had missed some days of Ramadan or missed some obligatory prayers or Zakat or other obligations, he is still obliged to make them up (after Hajj).

Allaah knows best.