A line is banded (slowed down) for a reason. Before the reason is determined and if necessary applying appropriate fixes, a DLM reset is not likely to provide a long term resolution.
Further there are a multitude of factors which contribute to a slow data speed - the important metric is the line sync speed reported by the router. Sight of your router stats would be useful.
Are you FTTC or SoGEA? If FTTC have you checked for the presence of a dial tone? The changed of data speed you report is not untypical of a one-leg-disconnect on the copper pair of an otherwise decent circuit. I dealt with this exact scenario of an elderly friend last week. They do not use the landline phone very much, internet was working fine ... so they were not aware that there was a problem until friends called them on their mobile because they were not picking up / answering messages left with call minder.
With SoGEA, the end user has no way of detecting this profile of issue ... and (apparently) the automated BOT does not detect one-let-disconnect faults - it needs a support agent to run the diagnostics.
@James_B - replying here has recalled my personal experience - can feedback on this gap in the automated diagnostic toolset please be raised internally.
Superusers are not staff, but they do have a direct line of communication into the business in order to raise issues, concerns and feedback from the community.
