Product: Credit card or prepaid card

I've been in talks with XXXX Best Buy regarding purchase and install of a home theater system since XXXX this year. We had a consult, they did a walk-through, work plan, budget and I paid a deposit of {$2800.00} toward the project. 

On XX/XX/XXXX I signed the sales contract. XXXX Citibank Best Buy offers 24 mos. interest free financing for Best Buy card holders. The offer for this theater project was 36 mos. interest free. 

On XX/XX/XXXX I reached out to Citibank Best Buy to request a credit limit increase for the Best Buy home theater system and install. I currently have a $ XXXX limit and {$300.00} balance on my Best Buy card. The PP for the theater system is $ XXXX. I asked for an increase to $ XXXX - only so upon increase I'm not bumped up against the limit ( prudent way to go ). Citibank Best Buy was giving me a hard time and I couldn't understand why. Eventually they asked how much I had in my cash/ saving account, to which I responded XXXX dollars ( less than the $ XXXX ). They then proceeded to do the increase to the exact X dollar amount I told them I had in cash. An increase to that amount came across as pointless, so I had a discussion with a supervisor there, citing the math showing I could comfortably pay the $ XXXX card balance off within the interest free 36 mos. At this time, said supervisor informed me that they too saw I could comfortably repay the card, that repayment wasn't the issue... and that beyond that, I also had a tonne of equity in my real estate ( which they said also strengthened my review ) ... but that rather the reason for their adverse action counter-offer was that I don't have sufficient experience handling a credit card with a limit of $ XXXX ( to them meaning 10 years or more they said ). 

My problem is I don't see how this is sound and reasonable banking for the following reasons : 1 ) My credit history goes back to XXXX. As for high limit credit cards, my current credit limit between my cards is $ XXXX ( revolving ) and my utilization rate is 5.5 %. 
2 ) The 2 highest card limits I have currently is $ XXXX and $ XXXX, respectively, ( totaling $ XXXX ). They're saying but I have had them for just over a year. True. But I've had cards before them and historically ( and currently ), I have constantly gotten calls from my CC companies trying to increase my limits to which I have always answered " NO '' because I don't see the point in having grandiose credit limits when I choose to only utilize 5.5 %. Now I'm being penalized for that? Penalized for being prudent and sound in my need and use of credit? 
3 ) Then from a common sense credit standpoint, I struggle to see the logic in giving me interest free increase to the amount that I have in cash. In a scenario where, say, the Best Buy home theater project did cost what I have in cash, why would I go with their interest free financing over XXXX mos.? I'd instead just use my cash and repay myself instead of CItibank Best Buy. It then just defeats the whole point of offering interest-free purchase financing. In fact, if the CItibank Best Buy purchase financing wasn't interest free, I wouldn't even be considering them in the first place - I'd instead just get a home equity loan which tend to have low enough interest rates. But why would I go the interest route when Citibank Best Buy say they offer interest free financing? 
4 ) I did get confused as to how ability to repay falls below experience handling a certain credit card limit in priority. The fact that I can repay the CC within the 36 mos. should matter more. And ... and ... in the very worst of worst case scenarios, if at the end of 36 mos. there is still, say, $ XXXX on the CC, I would then easily refi it at a relatively low rate with a home equity loan... BUT even if I didn't, and just did a balance transfer to my existing other CC so I'm not paying all that deferred interest, that would just mean my combined CC utilization rate will now be 17 %. 17 %. 
5 ) Speaking of experience, it was my impression that another thing that meant more than history of CC, is history of handling term debt. Around XXXX I had 2 unsecured personal term loans from 2 of the largest banks in the U.S. totaling $ XXXX and paid those off within 48-60 mos. Before that a vehicle loan $ XXXX ; paid off. My mortgage I've had since XXXX, paying down just fine. This is just baffling. 

So I utterly fail to understand how this is sound lending. And people that use credit prudently should not be penalized for doing so. I have a long credit history, a mortgage that's paying perfectly fine. I have XXXX late payments all my life having credit since XXXX. A tonne of real estate equity if we're talking worst case scenario of paying the CC off 100 % in 36 mos. Not to mention the offer is not for the CC to be paid off in 36 mos., it's pay it off in 36 mos. to keep the interest free promo. CitiBank Best Buy 's reasoning doesn't make sense, and while I wouldn't regard their actions as unfair lending practice, it certainly comes off as unsound and unreasonable lending practice. Can this be looked into and the reasonableness of this examined?