The area code (phone code) 05303 is assigned to 2 locations in Germany. Mainly you reach landlines in Wendeburg (Niedersachsen).
Note for calls from abroad: In addition to the German country code (+49 or 0049) you can omit the foregoing zero of the dialling code for Wendeburg. So you can dial +495303... and add the number of the phone line you want to reach.