It is not as simple as writing to the company and cancelling the wayleave.
It is in the deeds as an easement and therefore the only way it can be cancelled is either by a court order (which you are unlikely to get) or by agreement with the electricity company.
Even if there is no wayleave agreement in place allowing them to have this in situ, after 20 years they acquire the right to habit there either under the Prescription Act or under the legal doctrine of Lost Modern Grant.
I cannot see what the problem is with whoever you were dealing with because the electricity company will be aware of all of this.
Your solicitor should have pointed out to you that there was a wayleave in the deeds and that it’s not as simple as just cancelling it and asking for the post to be removed.
Most utility companies will remove such posts and resite them elsewhere or on the edge of the property or run the cable underground but they generally want paying for doing that and the cost can often be several thousand pounds.
With regard to it affecting the property value, I really don’t think you have an argument here because you bought the property with the way leave in place and with the eyesore in place and that must of been reflected in the value that you paid.
I’m sorry if this answer is unfavourable for you. If you speak to the solicitor that dealt with your conveyancing, he will confirm exactly the same
Can I clarify anything?