You can either call the local bar association for a referral (you usually get the next lawyer on the list who practices in that area) or you can search on martindale.com. A lawyer who has a peer rating of AB on martindale.com is considered to be a good choice by the ratings of other lawyers.
The lawyer referral number for the Clayton County Bar Association is (678) 467-6881.
Contact your state bar association, which is easily found through a Yahoo search engine. They each have a referral service.
You may be able to get action without even getting a lawyer. What the collection agency did is illegal. The Fair Debt Collection Practices Act (a law) & The Federal Trade Commission, FTC, (the agency to enforce that law) both are federal regulators of collection agencies. The FDCPA allows aggrieved consumers to file private lawsuits against a collection agency that violates the Act. The FTC may take action against a noncompliant collection agency, including issuing fines, ordering damages, restricting its operations or even closing it down. According to Section 813 of The Act, you could be awarded up to $500,000 in civil court after suing this debt collector. You should contact within one year a lawyer who is admitted to the Federal Bar in your state, as this is a federal law. Ask the lawyer if you can do it on a contingency basis, which could mean no or little upfront money and a percentage taken out of the award.