Validity Of Brother's Claim Over Locker

My late father (expired November 2015) and I are holders in SBI bank locker on either or survivor basis. In 2002 my father made a WILL making me owner of all his movables and immovable. My father was a Neuro patient since 2013. After his death my brother claims the Locker producing father's WILL made in August 2015 in his favor regarding the locker not having any mention of Will made in 2002, also it does not have his Signature but has his thumb impression. I enquired the Bank and found that in August 2015 Bank has received a lawyer's notice from my father asking my father asking to stop me from operating the Locker, so the bank asked me to get court orders regarding the locker. My brother has filed legal suit for claim over the locker on the basis of 2015 Will.