Your problem is probably caused by your international travel and use in funny spots of the world.

I have been cruising on the US east coast most of this year, using a credit card every few days or so. I discovered that my bank has a sort of policy to block my card every now and then when I am travelling. It is very anoying.

I call them and they immediately reactivate it, but it is still anoying. I finally told one bank representative that it was costing them money. I simply switch to a competitors card until I can call. They signed me up for a phone mail alert system that will notify me in advance before it is blocked so I can call and avoid the blockage. I haven't been notified yet, but the card hasn't been blocked either since they did this.

So my advice is to have both a good Mastercard and Visa and when one is blocked, use the other one and tell them so.

David