I am using 34 size bra, bit confused with A, B and C size bra

My bra isn't fitting right. It is wireless, and a 34B. The center isn't flat on my chest, and the back rides up slightly, but I spill out of a 32B. What

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Back Appeal® Minimizer Bra

34C Bras - Buy 34 C Size Bra Online at Best Price

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