In the 1990s, how did you pay your electric and water and gas bills before the automated robot voice on the phone?

By bank transfer

In the 90's, I wrote checks and mailed them to the utility companies.

most of them were issued every 3 months so no big deal to pay them and could budget accordingly.

first you had to hitch the team to the buckboard for the ride into town

The IVR was around in the 90s.

However, most people mailed the utility company a check or money order.  

Bills arrived in the mail. You opened them, read them, wrote paper checks in the appropriate amount, put the check and a stub from the bill in an envelope, addressed it, put on a stamp, and dropped it in a mailbox.

Personally, I've never paid bills via an automated voice service over the telephone. I knew people did that in emergencies, but not for all their bills.

I use to go to the bank and pay over the counter, they would stamp it as my receipt

With checks and mailed it in or pay at the store at their customer service desk.

Back then, a piece of paper called a bill was mailed to your house.  Then, you would mail another piece of paper called a check to the electric/water/gas company to pay the bill.

The same as I do now. With a personal check, monthly. In the mail.