Citibank Credit Card Complaint

Citibank Credit card department,

Application processing delay Florida

When we were in -, a vendor accidentally - billed a charge of - -, They issued a credit the same date, -/-/15. Unfortunately the - charges ( same day ) were billed at different exchange rates and were billed US $23.00 and US $22.00, but the credit ( same day ) was for US $22.00. When I questioned Citibank they were unable to assist me and explain how - transactions were for different amounts on the same day, they told me to refer to - - -. Does the - - - exchange rate vary by minute? This appears fishy to me.