Good news, today the engineer finally turned up (4th time lucky). He didn't bring any ducting materials and he suggested we try another path for the cable. We decided on the shortest possible run along the wall, then into the house through a newly drilled hole. This leaves about 10" of the cable exposed, and I've put some paving slabs in front of that to deter the rodents.
The internet connection is back to its original speed and my landline phone is working as well.
Now I jut have to hope that the cable won't break again.
