ERS insurance scam???

I got a letter from ERS saying my automatic deduction for insurance 6 months ago was $31.03 less than what was owed. ERS decides how much to deduct. NOT ME!
And, they say that if I don’t mail them a check for the payment of $31.03 in the next 8 days, they will CANCEL my insurance. And they didn’t even include a return envelope. And there’s no online payment option.