You could try filing a complaint via the Better Business Bureau (BBB). May not resolve the issue, but at least puts it on the record for others to see.
$250 is a huge amount of money to some and not others; it's all relative. From a financial aspect, depending on your specific financial situation, it may be better to simply pay straight away. Not paying the $250 and having it go to collections could result in an adverse entry on on your personal and/or business credit reports. That could easily cost you more than $250 in the longrun depending on your reliance on credit and/or other services, such as insurance, that utilize information on credit reports to determine pricing. Also, use of various Google services could be limited due to the outstanding balance.
On a related note, some creditors (and collectors acting on their behalf) generally don't report collections to the CRAs, but that's a fluid situation and can't be relied upon. There's always a chance of an old collection appearing years later, often at the worst time, such as when applying for a mortgage.
As a compremise, seek additional credit for future adword purchases. For example, buy $250 and get an additional $250 free, which would, in effect, make up for the $250 you spent. This would likely only work after paying the $250 you owe to their collections department, then contact their sales department to work out such an arrangement.
