What phone number is this , you state that a new number was allocated and that you tried to get back the original ( PSTN ) number , so which is it ? .
From what ‘landline’ numbers are incoming calls failing ? , are they BT customers, or customers of companies like Sky , Talk Talk , Vodafone etc .
There are some things that are just not under BT control, there was a post where a customer couldn’t get incoming calls from one particular mobile network ( that a family member used ) ultimately they had to accept a new landline number ( which worked from that mobile network ) because the mobile company were not interested in investing a call routing problem .
I suspect in your case , if you managed to get the original landline number reallocted , that information hasn’t been acted upon by every network operator and some ‘see’ that as a non working number .
BT essential is a social tariff and is technically no different to any other product, if you didn’t want FTTP , eventually even on the copper pair , the telephony would be via Digital Voice , and in that respect, having FTTP is irrelevant.
