This can be said of any RSP (Retail Service Provider or in old terms your ISP/Telco) as they all have a formal and contractual relationship with the NBN Co and we as customers do not.
Thus if you for example sign up for a new NBN plan with TPG, they will contact the NBN Co to have put in place the necessary pieces to allow the connection from your house through the NBN network to the TPG infrastructure. If you had a legacy system previous to the request that system will be disconnected and you will be “churned” to the NBN. The NBN Co after 18 months of availability in an area will inform your ISP/RSP/Telco that they are disconnecting the old infrastructure and then they will disconnect that old system regardless of your circumstances because that disconnection timeframe is the law for NBN Co.
If the NBN Co fail to connect you in the required connection timeframe they are allowed (I think it is 28 days) then your RSP is entitled to receive payments as a penalty from NBN Co but you as the customer are not generally entitled unless your RSP is also a Customer Service Guarantee (CSG) signatory and a Universal Service Obligation (USO) provider, the only one of these currently is Telstra. So as it is Telstra you are with you will likely receive a CSG payment if you meet the criteria which includes timeframe requirements.
I am not supporting Telstra here I am just explaining that Telstra may not be the culprit for your disconnection at all and had no ability to halt that disconnection. They may have sought to change you over and in that case it may be partly their fault. This will be looked at by the TIO and if Telstra was at fault they will be dealt with hopefully and if not and it was just the 18 month disconnection you probably won’t get much satisfaction at all, perhaps n apologetic letter but not much else.
@TheBBG The delay caused by the HFC issues resets the clock for the 18 month timetable for the areas affected and so the start date will be modified as each period elapses without change. Well that’s the theory anyway but is certainly something you can argue with them about.