Underpaid for a revised booking

[Neil40]

I am slightly exasparated as to where to turn for help. I had a booking for 4 people, which they then increased to 6 and asked if there was an extra charge, which there was and they accepted. 

I sent a revised price them and checked the day before arrival that it was still on their booking, which it was. However, I have only been paid the original booking fee. 

What do I do and how to I get the full amount. The guests have left.

Many thanks

[Helen3]

I would call BNB - full contact details  1st post - a few posts above yours in this forum.