How to ask for money nicely?

It's been almost 4 weeks since the fence at the back was completed and the neighbour (who said would pay 50%) behind us still hasn't contacted us regarding making a payment ... Mind you, he doesn't live there yet as his houses are still under construction but he does drop in at least once a week and we are pretty sure that he is aware that the fence had been completed...

Before we went ahead with anything we filled out the "Notice of Intention to Perform Replacement" form with all the details and included the quotes and everything. The quote we presented him with included everything apart from the plinth... However, once MrB decided that we would do the work ourselves in order to save some money, he rang the neighbour to ask if he would be happy with that, and if so he might even save some money. Now, MrB never mentioned how much of a saving there would be... The neighbour was happy for us to proceed. So, we went ahead and removed the old fence and concrete posts, paid for their disposal and also had the plinth done under the fence in order to prevent it from rusting etc...

The question now is... how do we work out how much money he owes us and how do we ask for it nicely? We've got the receipts for the fence materials and cement, but not the dumping of the old fence/concrete as it was disposed of by our concretor at the same time as other concrete which they had to replace... We were hoping that he would help us during the installation process in which case he would have only owed us for the materials used... but he didn't...

What should we do?

This is the notice we presented the neighbour with:

B