If the tech in effect went to the CBT and switched your connection with a neighbour, because each connection on the CBT is optically identical, if your connection didn’t work ( even though you were on ‘their’ CBT port ) and their connection continued to work even though they were on ‘your’ CBT connection, it’s going to be an odd ( unusual ) issue …possibly explaining the techs confusion.
The way GPON works is all downstream ‘data’ is broadcast by the OLT , and all ONT’s on the splitter receive that broadcast data simultaneously , each ONT ‘filters out’ the data addressed to itself , and ignores all the other data , the upload is different, each ONT uploads individually using ‘time slots ‘ so the headend knows which ONT is talking to it , if the data is corrupted within the headend for your particular upload ‘slot’ on the PON , then your ONT and the headend ( OLT ) cannot successfully ‘talk’ to each other , leaving you out of service , this could explain your somewhat weird symptoms, the optical path apparently fine , the ONT changed but still no service.
My suggestion ( if this hasn’t already occurred to the techs that visit ) is that your BT profile is ‘ceased’ , clearing out any potentially corrupted data from the system ( you won’t effectively exist on the OLT anymore) and then you are re provisioned as a brand new BT customer, with new data .
Obviously I can’t say with any real certainty this is the issue and my suggestion is the answer, but it’s certainly an avenue for them to explore…if that doesn’t fix the issue , it points to the actual headend electronics ( the OLT ) and that’s probably way above the visiting techs ‘ pay band’ , it may even need the OLT vendors engineers ( Nokia , Adtran ) to get involved
