Southern Water Not Accepting Meter Read

Hi
I'm with Southern Water and my payment system is pay on receipt of bill after southern take their meter reads every six months. I prefer to submit my own meter reads on a monthly basis to spread out the cost and to allow me to pay bills on what I actually use. I have considered using direct debit and payment cards but I got quoted £80+ per month. I don't use nearly this much water in a month and don't want to spend so much, hence the meter reads.

This month I tried to submit a meter read but Southern wouldn't accept it saying "The reading entered does not look right. Please check your meter and try again." I've checked, double checked and tipple checked my meter and it is correct. Don't see how it doesn't look right, there's no reason for it. The new reading is bigger than the last.

Anyone got any ideas how to get past this?