What is the ruling on one who exploited a loophole in a program to obtain a financial discount multiple times, and what is incumbent upon him after realizing that his action might be considered cheating?

You have done well in regretting your fraudulent act of registering fake accounts to benefit from the discount. Repentance is achieved by absolving yourself of what you took unjustly. This is done either by seeking forgiveness from the website owners, or by paying them the equivalent amount (2000 pounds) if possible. Otherwise, you should give it to the poor and needy with the intention of charity on behalf of the rightful owner. Ibn Taymiyyah held the view that whoever despairs of knowing the rightful owners should give charity on their behalf.