Any hope for a long line?

[#1]

I'm on a long line - it's nearly 3 miles to the exchange. However, the DSL checker gives me 'up to 2Mbps', and a range of 1 to 3.5, so I've been kinda hopeful.

However, recently the speed has plummeted. The downstream sync is 1728 but the upstream is at 64, and it's making it pretty useless. 

I know I'm on ADSL Max now, and interleaving is turned on. The router is sat next to the master socket, using a BT VDSL filter, and nothing else is connected to the socket. I'm running a TP-Link Archer D9 (the 2704n refuses to sync).

Is there anything else I can do to improve the line? Upload is pretty important to me, so 64k is pretty hopeless. FTTC has been coming for over a year, but doesn't seem to be happening soon.
The current ticket is 136490813.

My stats are:
up/down

sync: 64/1728

snr: 4/7.4

Attenuation: 31.5/63.5

Many thanks!

[#2]

Our tests were showing what's known as a high resistance issue which sometimes can be a internal fault.

You should be able to access the test socket still by unscrewing the VDSL faceplate and then the faceplate behind it.

[#3]

Thanks Matthew.
I'll try the test socket, though I'll still have a plug in a filter.
Is there anything else I can try while I'm at it?

[#4]

That's pretty much all you can do bar trying another filter.

If you can let me know when you've connected it that way I'll retest your line.