Sorry that happened, PWD. Hope things work out well for you, and thank you for sharing the information.
Closure or even decreasing the line for nonusage has become more prevalent with a number of banks recently, given the reports on here of people receiving CLD or closure when not using a card. A few people have reported a substantial CLD after only 4 or 5 months of non-use on a card.
It can be challenging to know what a lender's exact tolerance level is for nonusage, especially when you are told that everything would be fine as in your situation.
I use each of my cards once per month for a small purchase and while no one knows for certain, most likely it is establishing a steady, even pattern within their computerized alogorithm system. 