JVS, the others have given you good advice on handling your customers concerns.
We're having a record setting season and we've had a few complaints about statements. After several mild winters, most clients are used to seeing these amounts month after month. A few things I've learned.
Bill more frequently to reduce the clients "shock" when seeing the monthly total.
Daily invoicing or storm invoicing.
These will reduce "snow amnesia". Most clients don't remeber how many times or how much snow fell in a storm a month ago.