Product: Credit card or prepaid card

I have used Citi credit cards since XXXX. During the nearly 8 years, I've been a very loyal, used them regularly and routinely, NEVER missed any payment. 
I have three cards with Citi : 1. 'Double cash card ' with {$48000.00} credit limit, earned $ XXXX cash rewards, but not redeemed yet 2. 'Cost anywhere card ' with {$10000.00} credit limit, earned {$620.00} cash rewards, but not redeemed yet 3. 'Citi thankyou Premier card ' with $ XXXX credit limit, earned XXXX rewards ( equal to $ XXXXcash based on 1:1.5 rate ) but not redeemed yet Citi closed all my credit cards on XXXX XXXX ( Friday ) without a reasonable and fair reason, which 1. hurt my credit score a lot because {$83000.00} credit limit drops... ( I'm close to buy my own house, this is killing my credit score ) 2. refuse to let me appeal even there's no fair and reasonable reason given 3. intend to take all my {$3600.00} cash rewards and points rewards ( $ XXXXvalue ) away I will explain what happen and what I'm looking for help * I used the first two cards ( double cash & XXXX anywhere ) very often to XXXX all my personal and business office items, but used 'Citi thankyou Premier card ' less often. 
Since XXXX XXXX, I decided to use 'Citi thankyou Premier ' more. We have an 'stimulus program ' to award employees who perform really well with XXXX XXXX cards, I used to use XXXX XXXX credit card to buy XXXX gift cards from XXXX XXXX store, instead, I wanted to use this 'Citi thank you Premier card ' for it.

First, I called in Citi customer care and security team to report that I will start using this 'thankyou Premier card ' more often and focus on big transaction. 
Second, after they put in a note, I still had problem to make the transaction, I received security message every time, and I did call in every time to verify myself to make the transactions. 
Third, most importantly, I did ask them every single time to learn if it's ok to use this card for these big transaction, if not, I would switch back to XXXX, because I don't want to risk any misunderstanding or unexpected situation. However, all the security reps. I talked to every single time told me the same thing that it's fine, I just need to call in to verify myself for a while. 

HOWEVER, Citi cancelled all my credit cards on XXXX XXXX ( Friday ). I even called in to talk to rep. to purchase the monthly stimulus XXXX  gift XXXX on XXXX XXXX ( Thursday ), but they closed my credit cards the other day. 

Since I care about Citi, it's been 8 years, I almost focus all my personal and business purchase with them, never missed any payment. For switching using XXXX to Citi Premier, I even called in every single time to make sure if everything is ok. 

I know Citi is sensitive, so I was looking for the citi employees to guide me the right way. Customers wouldn't know everything, but instead of answering and guiding the customer what Citi doesn't like, Citi just closed your account which 1. hurt your credit score 2. cause you nearly {$7000.00} financial lost by taking away your 8 years ' cash rewards. 
3. I even still carry a balance when they closed my accounts EVEN WORSE, even they don't like a customer to call in every single time to make sure the way of using 'Premier card ', what's the problem with my other two credit cards, what is the good reason they closed my other two credit cards? 

This is so hurt, it's like you contribute solely and loyally for 8 years, but they just kick you away, take all your have, and don't give any reason, and even don't allow you to appeal. Is it a fair and a good way to treat their customers? 
I feel so depressed and desperate that Citi is a dictator, they do whatever they like and nowhere can control. I'm almost close to buying my own house, but they just hurt my credit score at this time. So disappoint and frustrated for them.