GCSE grades

Hi. I'm an international student, and was wondering how much of an impact GCSEs/ O Levels have on the application when it comes to Oxbridge. I've got fairly normal O level grades (considering O Level marking is different from GCSE marking) because there were some issues at hand. I've got 2A*, 4A, 1B, and a C in math (ahem) in my O Levels.

Hopefully, I will get A*s and A's for my A Levels, and I'm doing several super curriculars, I have been doing them since my O Levels, does that make my profile any better? Will my GCSEs/O Level grades be a deal breaker? Can anyone share their experience?

I'd appreciate any help. Thank you!