Probably best to hire a lawyer to respond and amend. As well, it is Charleston which is a notoriously "angry" field office. Although the leadership there has started to change their thought process, you may end up in a dog fight with them. You should prepare to have a lawyer prepare you for and attend the customary marriage interview when it arrives as well.
See an immigration attorney to understand why they may have sent you that Request for Evidence. It may have been an error by USCIS. In that case, I would answer the Request for evidence and tell them you are married to a permanent resident, and the visa is current. But if the visa is not current (because you filed it concurrently or at the same time), then you should have sent the I-130 first, and there is a possibility you may be eligible for adjustment of status if you have been out of status, unless he is a U.S. citizen. Again, see an immigration attorney for a peace of mind.
Hire an immigration attorney to correct this mistake and ensure that you don't make any more errors in processing. It will save you money in the long. Sometimes the cheap becomes expensive, and vice versa.