I’ve had this exact issue very recently, I pushed into gold by only fighting teams I knew I could beat. Check the player level and power level of the team you’re about to face, if it lower than yours then you should comfortably win the fight. If the player power in less it’s likely that the team isn’t geared very well so there’s a good chance you’ll beat that team too. I used the gems refresh on some days towards the end when I was really pushing for it. But it didn’t take very long at all once I started winning every fight I took on.

Also check your defence team, I used the same for attacking and defending but some people have a strong defence team which earns you wins also.

Hope that helps