CBM license keys should be associated with your account on my.vmware.com if you are a VCAN service provider with an active contract. At least, that's where I found mine. In regards to billing functionality, CBM works fine for us...for now. We are on 2.7.2 which supports vCenter 6.0 (although we are still on 5.5), but it does not yet support vCD8.20 or NSX 6.30 so we are using vCD 8.10.1 and NSX 6.2.4 for now.
I opened a support ticket with VMware to inquire about the future of CBM and was told 2.7.3 will be coming Q2 of 2017 and will support vCD 8.20 and NSX 6.30. As far as EOL, I was told it has not publicly been announced, but CBM for SPs will be retired at the end of 2017. Supposedly a future version of vRealize Business will be able meet the chargeback needs of service providers like ourselves including the ability to report on and bill for bandwidth usage, which is currently missing from the product as far as I can tell. In the meantime we will be looking at third party products such as OnApp as well so that we can ensure that we have ability to create custom reports for billing regardless of the future of Chargeback Manager or vRealize Business.