Electricity Bill and Credit

I left USA a year ago to work in Canada for my employer, now I need to return to USA to work for the same employer. Before I left USA, I checked all my bills and made sure every bill was paid. However, I was surprised to receive a letter from a collection agency for my last electricity bill ($23) I forgot to pay. I didn't receive the letter in time because I changed my address. So even I can pay the bill plus penalty (if any), it's still too late. I really don't want the $23 to ruin my credit. Anybody has similar experience? How can I solve the problem and repair my credit? Thanks a lot.