The problem now is you may have left it to late to have the case dismissed. The debt is statute barred as TLO says above. However this is your defence to the claim and you need to submit a replying affidavit ( sworn statement), drawn up by a solicitor, to the court and Belgard to this effect. Because the 28 days have expired since you received the claim notice I don't know if you have time to submit a defence. You really need to talk to a solicitor to see if it's too late to submit a defence. If it isn't you should be able to get the case dismissed.
FWIW a plaintiff must get a judgement to chase up a debt ie that is the first stage of the debt recovery. Thereafter they must return to the court to try and enforce the judgement eg getting an installment order against you. A judge will never make you pay what you can't afford and if you are of limited means the installment order, if it ever comes to that, would be manageable for you.