CC companies quick to block cards

for a while now, i've listed my mobile phone as my home phone on credit
accounts so they can always reach me if they suspect fraud... it seems they
are increasingly jumping on charges they deem 'suspicious' and will block
cards, or at least threaten to, very quickly.

Monday i got a call from Discover Security asking about 4 card swipes in two
days at Shell gas stations... well, yeah, that's what happens on long
holiday weekends when people travel. They couldn't even tell what cities
the swipes had been made in nor what the amounts were, only that they'd been
made. The call came about an hour after the 2nd of two charges on Monday.

None of the four charges has yet to actually show up on my account here a
couple/few days later. If i hadn't had my phone with me, i wonder if they
would've blocked it. Discover has called me several times like this when I
go motorcycle riding and might swipe it in 3 states in the course of a day.

i have read AMEX are overly quick to decline charges without even
calling.... sheesh, i wonder what constitutes 'unusual' use? Hope i don't
find out the hard way some day.

are other CC issuers as itchy? my one other card is First USA/Bank
One/Chase VISA, but i rarely use it.

i can't imagine being in a foreign country or something and suddenly having
my sole VISA or AMEX declined.