Wrong Number

Speaking of telephone calls, I am a victim of receiving wrong number callers. Anytime, my telephone rang and if I answer the call " hello fire department? " At first, I was frightened to hear the word "fire". I was wondering why my residential type telephone number became a telephone number of fire department office. I tried to check the fire department telephone number in the the city hall telephone directory and I found out that six digit number is the same with mine and only one number is not the same . My seventh digit is 8 while seventh digit of fire department is clearly 7 so we don't have the same telephone number but I am wondering how come all their callers come to mine. All of them dialling my own number. So irritating really.