Substitute for Formula

My milk production is dwindling and I tried giving my 7 month baby formula. He used to drink it when he was a new born, while I was waiting for my milk production to increase and then I breastfed full time. Now it seems like he doesn't like the taste of formula milk. He would spit it out and cry when we tried giving it to him today. What can I give him instead? Has anyone else experienced this?