The first thing you should do if you are accused of stealing someone's content is to take down the infringing material immediately. If you don't, you could be sued for copyright infringement. If you believe the accusation is false, you can file a DMCA counter-notice. However, you should only do this if you are confident that you are not infringing on someone's copyright. If you file a counter-notice and it turns out you are infringing, you will be sued and it will cost you a lot of money. When in doubt, speak to a lawyer.