Optus are well known for this lie. The period where Optus and Telstra can run competing fixed line product is called the co-existence period and it is always 18 months after RFS. Telstra abide by this for Telstra Cable and ADSL, but Optus cable got an exemption and try to only give their cable customers 3 months to switch because as soon as their customers connect to nbn they get a payment for retiring their network, This decision is solely Optus'. Also as soon as we went into lock-down nbn agreed to pause all end of co-existance disconnections so there is no need to switch due to anythign nbn has done. If the letter does actually say that nbn is asking for the connection then you shoudl challeng it because that is not the case, and the obudsmna has warned Optus about misrepresenting the facts before.