I this case it would help if you say who the DNO is that's refusing to come out, and more importantly, who is the energy supplier if it's not the DNO?The ones that I have encountered behaving like this are N-Power. They simply refused to come out to upgrade substandard tails from the head to the meter, even when I told them it was dangerous. The operative on the end of the phone just kept repeating "put your request in writing" like a stuck gramaphone record.
At the other end of the scale is our local DNO, Scottish & Southern who I have had dealings with both up here and darn sarf, and they have always been prompt, courteous, professional and efficient.
With experience you will learn which energy suppliers are helpful, and which are not. In the case of the unhelpful ones, you just have to wish for the seal fairy to come the night before. Then after you have done your work you can report that you have found an installation without a seal, and it's then their problem to either come and seal it, or just ignore you, either way you have reported it so covered your @ss
Perhaps a thread like this needs a quick straw poll with opinions of all the different DNO's and energy suppliers attitudes?