But even u key in rm50 but when u pull back the pump it will automatically calculate back the correct amount

at least thats my experience with my cc at shell

maybe check ur cc statement properly

i dunno how petron works but i can tellu for shell

for shell

u insert cc

type pin

take out

put in bonuslink card

take out

key in ur fuel amount or can direct fill

finish put back nozel and click receipt

then check amount on receipt

usuaully wont be wrong caz they do regular maintenance 1

even machine stuck or what if u dont pump it wont deduct

cant say the same for petron caz i seldom use