As the Sys-Admin for a relatively large e-commerce provider we have had our share of DDoS attacks. The first thing, is don't negotiate. Cut your losses and take the site down for a bit if you need to, regroup.
After that... switch your site to Cloudflare or a similar service.
After that... investigate if you want to continue using Rackspace for services. I suggest contacting me directly if you have questions, but suffice it to say we moved away from Rackspace because they and their data-center kept getting VERY large profile DDoS attacks which we were sometimes affected by even if we weren't directly targeted. We have had several months of service that they ended up paying for, for instance. Essentially Rackspace recently (at least their colo stuff) has not been providing 'superior' services.