I Bought Goodyear Tires, But Fewer Installments Were Applied Than Promised

I bought Goodyear tires on December 30th and was told that I could pay for them in 8 monthly installments using any credit card. I used my Yapi Kredi World card to make a purchase, thinking I could pay it off in 8 months. But even though the provisional statement said there would be 8 payments, today's payment was only made for 4 installments. My payment has doubled, and if I had known it would be reduced to 4 installments, I would have used a different card or maybe thought twice about buying it. I'm confused about how something that was initially stated as 8 installments in the provisional statement could suddenly be changed to 4. I talked to Yapi Kredi Bank, and they said that the place where I made the purchase has actually decreased the number of installments. This is strange because the initial statement clearly said there would be 8 installments. I'm really annoyed and thinking about making a complaint.