As Barbara pointed out, the OP has given sketchy basic information. I must point out that we look for clues to find alternatives and don't have special powers. Not providing information (such as that I set out in the
instructions) leaves those you are asking to help you to do extra work.
Thus, the SAYNOTO0870.COM has an extensive list of alternative numbers which have been built up of years and not because there is some magic formula behind it.
As has been pointed out, the 0845 number goes through to an IVR (menu) which allows access to emergency repairs outside of normal office hours. Numbers found thus far do not answer in this way.
Having looked at the numbers found so far, there is somethings quite striking; they all start 5720xx, 5721xx and 5722xx.
We have 572010, so perhaps 572000 is the first number in the block that Shoreline's office uses. The first in the block is often the main switchboard. ...Well what do you know but it is answered in the same way as the 0845 number !!