From 6000 increased to 50000coins to redeem £5

Every time I’m close to Redeem £5 , the cost of the coins to redeem increased.

At the very beginning, it's only 6000 coins to redeem £5, then increased to 12500. Now turned to 50000.

I will not continue with that coz I think when I'm getting close to 50000 coins, it will turn to a higher amount of coins to redeem £5.