So this is an FTTC service?
What is the source of the figures? Actual connection speeds or results from speedtests?
if the modem was connected while they were fiddling, or when you tried to reconnect wiring, the automatic systems may have thought the line was unstable (which is sort of was) and have slowed things down to try and get something to work.
NOTE: If anyone is fiddling with the wiring it is always worth unplugging all broadband kit.