Fibre installed 2-3 weeks -

[#1]

Hi,
I had my fibre installed 2-3 weeks ago.  The 1st day speed was excellent was giving me between 40-50Mb although I was on 38Mb package. 
After that speed changed.  I have checked number of times and its been showing 20Mb.  I have always been using wifi and my router stayed where it was. 
I had a online chat with online representative.  He said possible other wifi connection near interrupting my connection.  He asked me play around channels and see if anything improves.  I have tried but no change.
What should I do? 
Thanks
MS

[#2]

Try running the speedtest at http://speedtest.btwholesale.com/ . When it is complete choose the Further Diagnostics option and give it your phone number.  Post back the results that this shows.
That will help see if the issue is with the boradband or with the wireless.

[#3]

Note that test needs to be run using a wired connection.