Capital Billing Service Billing collection Los angelos California

I recently received a letter from Capital Billing Service stating that I owed money in the amount of 1098.90. This was unusual to me because: I do not remember agreeing to such a service., nor have they ever contacted me stating that I owed anything. 

I contacted the company upon receiving the letter and asked for the number of the company that I owed money too and he gave me the number without ever asking for the particular company, nor my name. 

The letter also stated that I am required to write a letter to them to respond saying that this letter was a mistake. So I definitely will be sending them a letter.