my flat has a BT Infinity branded phone socket Any advice?
As far as I am aware there is no such thing as "an infinity branded phone socket"!
Infinitity is a retail product sold by BT Retail. The BT equipment installed in the customer's premises is by BT Openreach and could not be branded "Infinity".
Have you tried the official BT checker? What does that say?
If you have looked in the spreadsheet - did you format the post code without any spaces? Is there a duplicate?
Ex <n>ildram , been to SKY MAX - 15,225 Download
BE Unlimited - 21,000 Download 1,200 Upload,
Moved house, now BE Unlimited 6,500 Down, 1Mb/s up - gutted!
FTTC Cab installation commenced 12th April - expect full 80 / 20 - bye bye BE, hello BT Infinity soon!