If anybody owes you money, then today, which is Thursday 31 January 2019, would be a good day to send them a statement to remind them of the fact. This is just a statement which you are entitled to send: it is not a threat.
First look at your bank account to check that they haven’t just paid you. We use an online bank account for collecting payments which we quickly transfer to some other account, so we can refer to it as a collection account or an in-and-out account.
Then send out the statements. Statements for large amounts get posted first class, and other amounts go second class. They should arrive on Friday or Saturday at the start of February.
We use SliQTools to do invoicing and statements, but you could use any other software. SliQTools is a standalone invoicing and statements package which is easy to use.
Our procedures minimise the risk of items crossing in the post, which can be irritating to the customer.