A threat letter from SP Services

It was exactly 11 days after the bill is overdue and I received this letter from SP Services threatening to disconnect my electricity and reduce the water flow rate. Hello, I owe them like $163.09 for 9 days, Considering the letter takes 1-2 days to be mailed out? A delay of less than 2 weeks for bill payment could result in me getting my electricity disconnected? For the past 28 months or so we have always paid on time and just this once?