When dealing with the issue of paying the VAback for overpayment, you should not go it alone. You should contact a veterans service organization that will provide a service organization representative, also known as a veterans service officer at no cost.
Service organizations include AMVETS, the American Legion, the Disabled American Veterans, the Veterans of Foreign Wars, and Vietnam Veterans of America, etc. or visit your local VA office.This should be done ASAP to insure a timely response to the letter you received from the VA.
It is always best to communicate with the VA in writing and not rely on telephone communication. In fact, it is advisable to send all letters to the VA by certified mail, return-receipt-requested and keep a record and copies of all letters and communications sent by you to the VA.
I suggest reviewing VA Form 21-0790 for more details about your rights to representation and a hearing in the case of possible overpayment.