Looks to me like you have a corroded phone line, high pings almost always means noisey phone line. The bad news is these lines always pass talktalk's own internal diagnostics so they will try to fob you off. What you need to do is demand the issue is escalated to an open reach engineer (not the talktalk bright spark engineer), tell them there is noise on the line. I had the same problem, after the new line was fitted my speed went from 3mbps to 23mbps. The whole process took over 1 year to do and talktalk gave me compensation of just £8. Unfortunately fibre isn't available in my area but I'm more than happy with my ADSL speed now.
