HSBC Bank Reward of $ 100 . New Master Card Account. Not honored by HSBC Torrance California

I opened a Checking account at this Bank sometime in last week of July 2017. Agent who helped me with the process, suggested that if i would consider getting a Master Card from HSBC , I will be given a reward of $ 100 , if I made purchases of $ 500 within a period of 3 months .I do have aletter confiming this. I complied with their requirement in timely manner. But no reward is forth comming.as of March, 1st 2018. I have contacted their credit card customor service. They have been giving me run around giving various not to give me $ 100.. Reasons given:are 1. $ 500 were not completed in 3 Months. I went over statement of account and proved to them the were wrong. This took more than 1 hour to convince them. 2.. Offer was not valid at the time of setting up os Current Account. . Told them I had confirmation letter from HSBC about this offer being in force on that day.I was told they can not do anything and that I should conact concerned Branch.They put me on hold for a hour with rthe above answer 3. I went to the Branch concerned with my issue a month ago.. They were good eough and tried to help me as much as possible. BUT NO CREDIT HAS BEEN AS OF TODAY . .