How can I get the money I'm owed from a customer

The correct solution is to ask the client to state in writing the alleged faults, and offer to repair the faults free of charge. This is legally both of your obligations. If she refuses to let you repair the work, then you must request a copy of the quote for repairing the work, she is legally obliged to provide this. She will then deduct the amount of the quote from the cost of the work due to you. If you do not accept the quote, or there is no quote, and you are happy your work was of good standard, then you stand by your invoice and inform her she has 14 days to pay or you will issue a summons. You will need an expert, a friend in a similar trade for example to visit and confirm the work is good, or bad. But you must be sure you are in the right. It is easy to either invent mistakes in your mind, or invent flawless work. If she gets a quote to repair the work, give in and swallow your pride. If she does not, then she is faking it, then sue. Hope this helps. Sadly, many customers try this trick when the work is almost finished. Paul