You're best off speaking to our Financial Services team. They'll be able to take a look into it for you and help organise a payment plan. You can reach them on 1300 308 839 Mon - Fri: 8:30am - 7:30pm and Sat: 9:00am - 6:00pm.
Hi @Domb88, well done on taking the bull by the horns and takling the debt. A couple of things you should also be aware of:
1) You should get a free copy of your credit report (websites will try charge you or offer bogus 'premium' reports.) but we are all entitled to request one free once a year. Read here for how to get one. Check to see if you have any black marks.
2) Optus my have sold your debt by now. Generally after a number of months of non payment they will sell the debt to a third party and so will not be interested in you paying it off anymore. Hopefully they can refer you to the debt collector involved. Note that there might be little benefit in contacting and better to wait until they contact you and ask for the (original) debt to be repaid. After six years of no contact the debt generally gets expired. But that's just my opinion, its generally better to settle debts than not.
As mentioned first stop is the Optus Financial team and they can see if they can find anything. Its quite possible they'll have no record and you can put the matter to rest. Perhaps just ask the team if there is any outstanding mony owed on your name rather than tell them you owe them money straight off.