Your S/N ratio should be around 6 and having to double it to 12 for a stable connection sounds to me like you have a bad line connection or interference from other electrical equipment e.g. satellite box or cordless phone placed too close to your modem/router.
The other possibility is a bad microfilter that separates the telephone and broadband. Newer master sockets have an inbuilt filter and there are 2 sockets, one for the telephone and the other for the broadband so microfilters are becoming obsolete.
You need to identify which type of faceplate is installed and BT has a guide here to help connect your TalkTalk modem. http://bt.custhelp.com/app/answers/detail/a_id/40812...
As you will have disconnected your modem you need to allow time for the DSLAM line training to kick in. This can take a few hours/ days so do an initial speed test and then see if things improve over the next few days but do keep the cable in the test socket and the modem powered up otherwise the line training will fail. You should never power off your modem at night for this reason.
If there is an improvement using the test socket connection then your faceplate needs replacing and these can be bought on-line but make sure you upgrade to the latest BT faceplate and not a cheap clone! Browser search “Genuine BT Openreach MK3 VDSL/ADSL Faceplate/Filter NTE5a Master Socket Back box” with the quotes and see what is available.
If there is no improvement then the fault is outside of the house and you will need to book an engineer visit. There should be no charge for this as anything beyond the master socket to the exchange is TalkTalk’s responsibility. They will probably send a BT Openreach engineer to repair the line.
Last week my telephone line went dead and I called TalkTalk on 02034415550 and after pressing numbers for all the options I eventually got through to a help desk. The following morning an Openreach engineer arrived and repaired the external line fault. Worst IP ever? I think maybe not.
I am 100% recycled material of which 90% are microbes. I am therefore never alone.
Edited by microtan (Thu 07-Jan-16 22:44:40)