I have had issues where I have had extremely bad speed issues for certain periods which seem to just go away as quickly as they appear..
I must say that the PN team are always on the case if/when I have anything to question about anything relating to my service.. Especially on this forum where the PN staff must monitor as they get back to you almost straight away if any users express any problems relating to PN services.
I have had speeds from the BTW speedtest down to as low as 14.4/14Mbps (approx) and then by the time I have completed the reporting of the problem the issue had almost gone completely away except for a - (minus) 3Mbps drop off my BTW "Max Attainable Estimate" which did originally show 73.3Mbps now its 70Mbps but that's just nit picking.. My official speed estimated for which my line could handle on the ADSL Availability Checker showed:
32Mbps / 6.5Mbps Well this was completely under estimated and almost doubled upon request for IP Profile to be updated..
Anyway, back on topic
I don't know if you have tried this but I found that after 21days of uptime I just done a quick disconnect/reconnect through my router, thinking this may help to clear the line (or whatever) in fact when I did reconnect my ping time had gone from the 25ms mark down to 10-18ms mark and shortly after my speeds went back to 'normal'