I posted a thread about this on the budget board a month or two ago. I have a credit score around 800. I have two cards with Chase. One had a limit of $18,500 and the other was $19,000. I put almost everything on my cards then pay in full each month. I usually only put $1,500 or less on them each month. But in the fall I was remodeling my kitchen and charged my new cabinets, countertops, flooring, etc. I was racking up a ton of points. Then one day I went online to make a payment and the available credit caught my eye. It was about 1/2 of what it should have been. I checked my limits and they had lowered them both to $10K. And they did it with no prior notice. If they'd done it in the fall when I was charging all the kitchen stuff, I would have easily gone over my limit and racked up some fees. I don't need the high limits normally, but it will hurt my credit score because it raises my debt to available credit ratio, which sucks because I'm not any worse of a credit risk now than I was before.
So you aren't alone.