Cable Forum - So slow Virgin performance

Hi all
Earlier this year I upgraded to Virgin M250 package, expecting to see at least the guaranteed minimum speed of 132Mbps. No such luck, despite being on the phone to their so called technical help for what seems like hours and hours. Reboot this, press this, swap these, tighten this. The same crib sheet every time. They insist there is no problem their end or with their router. So I've been trying to problem solve at my end to see if they are right.
My router is downstairs near the Virgin TV box and nearby TV. No problems there. My 2 year old Dell is upstairs and was linked wirelessly to a TP link booster that plugged into the mains wall circuit. The signal strength seemed to be good but download tests showed speeds never above 75mbps. I tried several test sites and although the results varied, 75mbps was achieved just once.
I ditched the TP link wi fi booster and installer a TP link AV1300 passthrough powerline kit. This is two units that plug into the house sockets, one by the router and linked via a Cat 6 ethernet cable to the router, the other next to my pc and again linked to the network card via a Cat 6 cable. Apparently it's capable of a gigabit transfer rate. The network card inside the Dell is a Killer E2400 Gigabit controller and the speed capability is in the name.
On my pc network I went to the Virgin router. It comes up as an Arris TG2492LG-85 router. I logged into it using the original set up details and found that it can display speed information. Apparently the router is receiving at 1000mbps and passing that on to my pc via the ethernet. However, the online speed tests show an improvement, 95mbps download spiking to 102mbps, but nowhere near the Virgin minimum guarantee of 132mbps.
I am at a loss and another £60 down for the TP link kit. Any ideas out there that won't cost me again.