The police have 6 months from the date of your offence to lay a charge. They're now outside of that time frame, either your bloods came back below the limit or there's been an oversight. Now that you're outside of the 6 month time frame it wouldn't hurt you to ring the police station that you were brought to when you were arrested for an update on your case. After 6 months the result can't be used in court, so unless they've been sending correspondence to another address you're in the clear based on what I've read on this forum about the time frame they have to lay a charge against you.