Product: Checking or savings account

On XX/XX/XXXX, I made an online transfer of about XXXX from my Goldman Sachs Marcus account to my other bank account I'll call " B '' ( a major XXXX XXXX ), as I've done many times over several years with no issue, from this same Marcus account to this same B bank account, including for much larger amounts. After the XX/XX/XXXX online transfer had gone through and showed " COMPLETED '' on both ends, both on the Marcus website and on the " B '' website, on XX/XX/XXXX I verified this with " B '' bank over the phone who verified it as completed, so I then made other transactions with those funds. 
- The next day when I logged into my " B '' account I saw a red banner at the top of their website saying I was negative XXXX in my account. 
- I called " B '' bank and they were similarly confounded, said even though the transfer had shown complete, Marcus had taken the XXXX back and I needed to call Marcus about it. 
- I called Marcus and the first person authenticated me by texting me a code which I verified, and then asking me a security question which I answered. The person then said they couldn't tell why my account was frozen and they had to transfer me. The next person said they couldn't authenticate me THOUGH I'D JUST BEEN AUTHENTICATED and would not tell me why they froze the account unless they could authenticate me! 
- They said they couldn't use either of my two phone numbers on my account for authentication even though I'd had the one phone number for over 15 years and the other number I'd been using for authentification with Marcus since XX/XX/XXXX and had just used it for authentification with Marcus moments previous ( the same number I used for " B '' bank and 5 other banks with zero issues ). ( Id called both phone companies who said both phone numbers were working fine, connected to me, etc. ) - They said my only options for authentification were to " MAIL A PACKAGE TO MY XXXX ADDRESS '' OR CLOSE MY ACCOUNT and have ALL the money in my account sent to the bank I had linked on my Marcus account- WHICH WAS THAT SAME " B '' BANK ACCOUNT. I'd never heard of any bank paper-mailing someone a " package '' for authentification, especially in this digital age. I said I didn't want to close the account and explained paper-mailing me a " package '' for authentification would not work for 2 reasons : " B '' bank expected that XXXX back in my account immediately, and I couldn't wait for a package to be snail-mailed to my XXXX  address. Also, I'm going to school in XXXX, so it would take even longer ( and be unsafe ) to then have it mailed to me in XXXX. 
- I explained again, as I had numerous times to a number of people at Marcus over several phone calls, that I did not have the cash to cover that XXXX in any other account and had to get my Marcus account unfrozen so Marcus would allow the transfer to " B '' bank. 
- I kept asking if there was anyone else who could assist me with authentification so I could get the XXXX back to " B '' bank, and even called back several times to find someone reasonable to help, and each time was told those were my only two options, " mail a package to my XXXX address '' for authentification or CLOSE MY ACCOUNT AND SEND ALL THE MONEY IN MY ACCOUNT TO THAT SAME " B '' BANK ACCOUNT! They repeatedly refused to tell me what the issue was, why they taken back the money when on their website it had shown the transfer was COMPLETED, wouldnt help me in any way. Their customer service was unhelpful, unprofessional, rude and irrational. 
- Since the only choice they left me to repay " B '' bank in time was to close my Marcus account, I did close it, and they then sent ALL my money to my " B '' bank account! THIS IS SECURITY? THEY WOULDN'T ALLOW THE XXXX TRANSFER SO THEY SEND IT ALL? 
This was incredibly stressful and frightening. I've never experienced anything so irrational in banking. I'd like Marcus to be held accountable for this so others don't have to go through what I went through, and would like to know why Marcus is allowed to run a bank with such deplorable, fraudulent and highly unsafe practices?