If only your Citicard is affected, and if you have the same phone number, and if you have logged into Citicard and checked your alerts settings to make sure all is in order and the phone numbers are correct, and if you also checked your ‘blocked’ list, and if everything else is working, then it simply cannot be an iPhone or Apple issue.
If I were placing a bet I would put my money on your Message app blocked list.
Block, filter, and report messages on iPhone - Apple Support
Also check Settings->Apps->Messages->Message Filtering->make sure Filter Unknown Senders is OFF. However, if it was ON every message from a sender not in your contact list would be affected, not juts CitiCard.
Block phone numbers, contacts, and emails on your iPhone or iPad - Apple Support
See if any of these support documents are of help.