Product: Bank account or service

Complaint : Citigold checking account service denying my {$400.00} Cash Bonus On XXXX XXXX, 2015, I open a Citibank 's Citigold checking to earn {$400.00} Cash Bonus with promotion code XXXX through XXXX. The promotion requires 1 ) Open a new consumer Checking Account in The Citigold Account Package by XXXX/XXXX/2015. 2 ) Make an eligible deposit of {$50000.00} or more in new-to-Citibank ( R ) funds into their new Checking or new or existing Savings Plus account within 30 days after account opening. 3 ) Maintain a minimum of {$50000.00} for the next 30 days to receive their bonus. 
I received the welcome package on XXXX XXXX, 2015 and mailed the signed signature card back to them on XXXX XXXX, 2015. On XXXX XXXX, 2015, I made a deposit of {$51000.00} into my new Checking in their XXXX XXXX branch and the deposit of {$51000.00} was soon shown in my online account page. 
On XXXX XXXX, 2015 when I randomly browse my online Citi bank account, shockingly I found that the balance became XXXX on XXXX XXXX, 2015 through Teller Withdrawal, which I did not authorize. After I contacted Citibank customer service, I was informed that my account was closed by bank end department and they authorized the withdrawal and a cashier check was sent to me. I was directed to New Account Servicing for the explanation of the closing of my account. I was told that it was due to an error on my signed signature card. While identifying myself as the primary owner of the account and sign it, I accidentally checked a box for additional user and signed my name next to it. I was told because of this error, my account was closed. 
I need to point out that I mailed the signed signature card on XXXX XXXX, 2015 and made the deposit on XXXX XXXX, 2015. In other words, the signed signature card should have already arrived before I made the deposit. But I was not notified any problem with my account when I made the deposit. One may debate that their New Account Servicing does not review signed signature cards that fast. I understand if it may take several more days. However, it took them 25 days to identify the error. 
One may also debate that I need to wait until my signed signature card is approved before I made the deposit. Their {$400.00} promotion requires that I need to make an eligible deposit of {$50000.00} or more into my new Checking or new within 30 days after account opening. My account open on XXXX XXXX, 2015 and their identified the error on the signed signature card on XXXX XXXX, 2015, which is after 30 days. I would have missed the promotion window. In addition, in their welcome package, they did not specify I should wait until my signed signature card is approved before I made the deposit. 

My point is that since the {$400.00} promotion requires 1 ) Open a new consumer Checking Account in The Citigold Account Package by XXXX/XXXX/2015. 2 ) Make an eligible deposit of {$50000.00} into their new Checking account within 30 days after account opening ; 3 ) maintain a minimum of {$50000.00} for the next 30 days to receive their bonus, I satisfied the first XXXX requirements. I do not satisfy the third requirement by 5 days because they took the liberty to close my account. This action makes me suspect that they close the account deliberately right before I satisfied the third requirement in order to avoid paying the {$400.00} cash back which I deserve. It also reminds me of the so called error that I made on the signature card. If I checked an extra box, I put my signature there, not somebody else. What problem does that constitute? Even if my error voids the signature card, they could have contacted me and send me another card to sign. How does that cause the close of the account? Even if they need to close my account, why did they keep my money so long? I also read on the internet that there are similar cases occurring with their Citi gold promotion, which make me suspect that they use this as a strategy to avoid pay {$400.00} cash back.