Upgrading to fibre, wiring unusual

[#1]

Last week I ordered an upgrade to fibre (online, not by talking to anyone at Plusnet). I haven't received any emails about it or got any hardware from Plusnet but there's a service notice on my account that says the change will take place at 2am on Thursday 16th.

As I understand it, this is done by customer self-install now. Because the wiring in my house is a bit unusual, I'm concerned that there may be a problem with setting this up. The wiring is unusual for two reasons: an old ISDN connection and rewiring after the house was flooded a couple of years ago.

First, the ISDN connection. This was literally last century. When the ISDN connection was installed in the house, there was already a telephone line but they dug up the lawn and ran another cable to the house. There's some connection boxes on the wall outside with some untidy wiring going in different direction from it. The ISDN was disconnected years ago but the wiring was left in place.

Secondly, the flood recovery. The telephone connections were opened up to dry them out and I'm not sure which is the master socket and which the extension. They are just a few feet away from each other and we think the covering plates may have been interchanged. Is that possible, given that the phone works?

With this uncertainly, I'd rather have an engineer involved, in case the new fibre doesn't work but by then the current connection has been removed. Any suggestions anyone?

Thanks,
Brian

[#2]

        In case anyone else has a similar problem, here's some information about what happened. This did give a problem; I installed the hub on the day but the speed stayed under 11. I had several online chats and other contacts with Plusnet support staff but no-one got to the bottom of it. A lot of time wasted. A bit of extra training needed here perhaps.
       Eventually I was in contact with someone at Plusnet who ran tests on my line, found there was something at fault and arranged for an engineer to come. The BT Openreach engineer re-wired it. He said (I think) that the connection coming into the house was split into three. That would make sense - one normal phone line and two lines for the old ISDN connection. Apparently, the issue may have been star wiring; I don't know the implications of  that  but I found a vaguely relevant thread on a BT forum (community.bt.com/t5/Phones/Ancient-Wiring-Plan/td-p/566435).
     So thanks to the person who sorted if out - finally, after a month or so, download speed is about 33Mbps.