are they allowed to immediately try to recover the debt or must they go to court first?
They can try to recover the debt, either directly or through a debt collection agency. They do not have to go to court first; courts are for the resolution of a dispute and right now there isn't one.
If the consumer disputes the debt (which they should do in writing) then the debt is held in abeyance until the dispute is resolved. While in this state debt collection must stop and the debt must be noted as disputed on any credit agency checks. Dispute resolution may be through negotiation, litigation, mediation, arbitration or a statutory mechanism (e.g. involving a government agency or ombudsman if applicable).
If the supplier chooses litigation then they must go to the court and summons the consumer; stating the basis of their claim. The consumer is then entitled to mount a defence.