Your credit score would drop because of your credit utilization. Your credit was maxed out or a significant portion of your available credit was being used.
It works like this, if you have lets say, 50% or more of your credit card maxed out it will ding your score because its shows high credit card balances in relation to your available credit on the card = you are using a significant amount of your available credit for some reason, which to a credit score may mean you are having finanicial issues, so the score gets dinged. Also before your trip you asked for an increase in credit and was denied by your credit card company. Another ding/maybe better said another inquiry was made.
If you owed the same amount of money on that card but had two other credit cards totaling maybe $30,000 worth of available credit (just as an example) , it would show the credit agencies that you were only using lets say $4000 of that $30,000 so would actually show you are very credit worthy and in good shape. But showing a $4000 debit on a $6,500 credit shows a significant credit risk.
Of course I am going to disagree with some in here (nothing new*L*) this has nothing to do with the credit card issuer, in this case Citibank.
Your best bet is to keep the Citibank card forever, pay it off, let some time pass and get another line of credit with another card. You should have 3 cards in all. Keep them clear of balances, or if you must, not more than one card with a balance.
Citibank does not control your score and has nothing to do with your score anymore or any less than any credit product.
NEVER EVER cancel a card that you had a long time, it sounds like you maybe newer to having credit, always keep the card you had for the longest period of time and never cancel it. It shows the credit agencies (which are just computers) that you have had long term credit.
Even though lets say a bankruptcy may only stay on your record for 7 years, if you have a credit card that dates back 17 years it will show that you most likely never had an bankruptcy in those 17 years because you still would not have had that card if you did.
My longest card dates back over 30 years. I don't use it often but will not cancel it.
BTW, I LOVE my Citicard, I get back 2% cash of everything and anything I buy. I have had this card also for years, if I ever bought anything where I was having an issue with a seller, literally as fast as I could contest the charge on line Citibank Credited me. If you don't have a 2% back Citicard maybe once the dust settles you can ask them to convert you. There isn't any product on the market in the world that someone hasn't had an issue with, as far as cards go Citi is my favorite. Any time I ever had an issue with a seller, bam, no questions asked from them, I dispute it online and my account was credited in many cases, without an investigation.
I am not sure if this treatment is because of my credit standing which is outstanding on the FICO scale.
I carry a total of 4 cards only one of which I switch around based on what deals they will give me, but always keep the card I had for 30 years.
I have such sweet deals that its almost stupid.
Though Congress is trying to end that by limiting transaction fees to sellers and stores which would affect cash back and the IRS is also wanting to tax cash back as well.