It's impossible to say why there is a delay.
BT have declared MBORC in various regions due to poor weather and I suspect more will be added to this over the next few days due to the flooding in various parts of the country.
If you are in a region that is classed as MBORC, or has recently had this, there could be a backlog.
If not, it could be there is a reason for the delay which is not a quick fix.
As Bob says, regardless if you were with a LLU supplier or not, it is still Openreach
(the same people that will come out on behalf of Plusnet/your telco provider) who will attend.