Many hotels will tell someone who calls whether someone is a guest there. It seems to be common practice. However, signing in with an alias is often done for celebrities so why not you?, or notations are made to not give out any any information if anyone inquires. Do you know whether the person giving out information about you was on the front desk or a phone operator? There could have been a mix up, with one not knowing that you wanted anonymity. Definitely talk to the GM, not just someone on the desk or a supervisor. You need to go high. It does make a difference. Low level hotel workers may not pay appropriate attention to you, or just try to appease, but if the GM knows you're a regular guest, that carries weight and workers will follow his or her instructions or face reprimand or worse.