If you have tested an old fashioned corded telephone i.e. works from just the power over the telephone line and there is no dial tone at the test socket then you have shown the issue is not within the property (exception would be if a previous tenant had some how broken the wiring, e.g. smashed furniture into wire breaking it)
£250 sounds expensive particularly if as the listed charge is half of this
Personally based on what I've heard from other Home Telecom users I'd use this as an opportunity to walk and go elsewhere. The fact they are quoting inaccurate pricing is enough to make me say - run away while you can.
Your £69 installation fee should have included activating the telephone line and every indication is that this has not happened.
If not sure, a visit to the citizens advice bureau to find out where you stand legally may be worthwhile.