I am going to guess that there must have been a period of time (like a year or something) with no activity. Maybe you used it once or twice recently, but there must have been a long gap of you not using it at all.  After the gap maybe you maxed it out. Closing your card if you were using it every month and paying in full for "inactivity" simply does not make sense. If you were using it all the time and you called the corporate number, they would have seen the charges every month and saw a lot of activity. I just don't get it. There is stuff you must be not telling us.

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Starting Score: 693 TU FICO, 679 EQ FICO
Current Score: 748 TU(12/12), 771 TU98 , 824 TU08 FICO, 776 EQ FICO , 735 EX(9/12) FICO
Goal Score: 750+, but shooting for the 800's
my wallet: Hyatt Visa Sig ($23K), B&N World MC ($17.3K), Amex RP Gold (NPSL w/ S&T), Hilton Surpass (10K), Freedom Visa Sig ($8.6K), Discover It ($8K), Amex BCP ($9K), FNBO Visa (13.1K), Citi Dia Pref MC ($3.7K),Sam's D ($8.5K), Walmart D ($7.5K), JCP($5.3K), Dicks MC ($2K)