From  recent personal experience – as the disgruntled supplier – I suggest:

If they owe you

• Be reasonable.  Times are tough, people generally do the decent thing.  Anyway hitting hurricane force immediately leaves nowhere to go.
• Be persistent.
• Know your rights.

If you owe them:

• Don’t hide.  Ignoring email, phone messages or carrier pigeons sent to chase the debt won’t work.  Like Arnie, they’ll be back.  Keeping people in the dark  infuriates them.  There’s good advice here.
• Be honest, explain, offer to pay a bit at a time to show good will.
• Get  help.
• Remember, no-one believes “the cheque’s in the post”.