Chargeback issued by client

So I just noticed that a client has issued a chargeback for a commission ! They didn’t message me or give any explanation and it is way before the guaranteed completion date 😭! I have sent them a sketch a few days ago and continued working on it , I have a few other comms along side my actual job so I will admit I’m not the fastest ! But I’m not sure what to do in this situation as I sent them an update they have seen it and then upon checking emails realised they have issued a chargeback an hour or so before sending the update :/ they have now seen it and are not responding ! Not sure how to go about talking to the client about this !