Ba@@**rd,
WTF's going on here? Where's his business registered? If in UK and one has a contract, that has to be Small Claims Court surely? This has a side-benfit at getting a CCJ against the Company, and a record which is publicly visible.
If it were me I wouldn't shrink from sending a recorded-delivery mail giving 14 days for settlement - or SMC to be effected. It only costs £100 and you get that back if/when you are successful. Me, I've had enough of all this BS. If a contracted agreement is delinquent I send a letter saying that they might like to discuss this in court since I am a VERY small business (me) and I've got a family to earn for.
What do you think, team? ~ VFR