Stop auto insurance letters?

Question

Is there an effective, legally backable way to stop an insurance company's continuing letters requesting my business?

Answer 1

If in the USA and if it is first class mail, don't open the letter write on the front "Refused".  They will get the letter back.

Anyone can always refuse any (unopened first class) mail they receive and it will be returned to the sender

Answer 2

Write on the envelope "return to sender" maybe they will have to pay postage again to get it back.