Plusnet Fibre No Good For Xbox One Gaming

[#1]

Xbox one does not work on plusnet fibre - keeps turning message on "nat strict"  which stops you playing with your friends my son had his new xbox for xmas and it won't work on plusnet - rang tech support they said they "don't cover this issue? " even spoe to a supervisor and she confirmed the same even sent me an email - no help whatsovere i feel i have signed uyp for something that is not "fit for purpose"
adie:red changed all caps title and post as per link:rules

[#2]

Sorry to hear of the problems you've had. We have an XBOX One here in the office and haven't had any problems connecting that up or playing online with it (the PS4 is a different matter and has already been replaced).
Which router do you have and what have you tried so far to resolve this?