There are several alternatives to issuing legal proceedings where the customer accepts that money is owed but disputes the amount due.
Mediation/debt compromise: an independent person helps the two parties to find a solution to the problem. Any agreement reached is entirely voluntary, which means the parties cannot be forced to stick to it. The claim may still end up being resolved through the courts and your debtor will need to be willing to engage in this process.
Arbitration: an independent arbitrator hears both sides and makes a decision. Arbitration is binding on both sides, and the parties cannot got to court after an arbitrator has made a decision.
Statutory demand: the creditor issues a statutory demand, warning of an application to court for the formal winding up of the customer’s business, if payment is not made within 21 days. This is quite a radical step and only to be taken if the relationship with the customer has broken down irretrievably.