On 1 March I receive the 45-day notification stating that higher interest rate will be charged on any new transactions made after 14 days from the date of the notice. On 10 March I made a $100 purchase. My question is till which date the regular APR will be charged on $100 purchase amount?
Since your purchase was made before the 14 day deadline, you'll receive the regular APR until the 45 days have elapsed. Call you credit card company. They can provide the exact terms.