Discover Bank Account Or Service Complaint

Discover Bank account or service department,

Savings account Account opening, closing, or management Arizona

I had opened a Discover Savings account using a promotion. I fulfilled all the terms and conditions mentioned in the promotion code including entering the promotion code also. Just to be on the safer side I got a cross confirmation from Discover that i will get the promotional bonus also-i had the email conversation via secure message center. Later when i am expecting that i will get the promotional bonus - i come to know that Discover is asking me whether i had entered promotional bonus or not? May be they are having second thoughts now. And most interesting - why they are deleting the messages like this? I can see that on the website they have mentioned that " all messages are going to be deleted after 30 days '' ... why??? In this age of Bigdata and analytics ( where storage is so cheap ) and moreover for legal reasons - financial institution should not do something like that - why DFS is not following it?