Yeah that is an issue a lot of people have.
Keep trying.
If you can't get past it, email EA and they tend to be quite helpful, they gave someone on here a free game IIRC.
That was probably me.

This very game and problem in fact!
Yeah, keep trying (for every try an order number is created in your profile, so they can see if you're telling the truth) but if you find you keep getting "We are unable to process your order. Please verify your information and try again" then contact support.
You're trying to buy a game and give them money, after all. Don't worry about them sorting it before the sale ends. Worst case scenario they could process your order for the price you were trying to pay - best case scenario, which I experienced, is that they could give you the game free even though the price had reverted to £29.99.
When you're on the EA store site there's "Customer Service" at the top, the page to contact EA support is through there. Drop them a message describing your problem. It's also worth mentioning their site bandwidth too as it's slow as hell!
What happened with me is the response from support was unsatisfactory. I received a survey asking me to rate my experience, which I did poorly because it didn't resolve the issue. Then I got a response from EA escalated support, who asked me to describe my problem again. I did that, and next thing I knew he'd added the game free to my EA account.
Great way to treat genuine customers imo.