The phone is free unless you have opted for the $5-$20 extra packs. Just contact Optus on live chat and ask them to remove the bolt ons.
Its easy enough to get a wireless phone for under $150 you can use in any room if you want to try that option.
Ty, will try again I guess, I spoke to someone in billing yesterDay and explained to her we can't use the home phone to cut it off, because when I signed up I did say I wanted the home phone so now are being charged $12.75 per month for rental, and calls. But when NBN technician came he said I could not have the NBN modem next to the phone and it was put in another room. The person on the phone said I didn't need to do anything, I was paying this amount a month and that's all. This is not true, on my first bill I was charged the plan amount and then the extra. So hard to explain anything to these people on the phone. I must have spent 10 hours the last week trying to get the NBN activated to sorting this mess out. I don't want to buy a cordless phone, I had one before and chucked it out, anyhow with 4 mobiles in the house we don't need a home phone now.
@Disney What NBN plan are you on? Most NBN plan has a landline attached(home phone), like @petergdownload unless you ask for any extra bot on, then it is part of the NBN plan. Getting a cheap cordless phone would let you use the home phone around the house, eg https://www.jbhifi.com.au/products/uniden-dect1715-cordless-phone?variant=14611779551330