A few years back I changed the utilities for my son when he bought an apartment
I called Endesa the electricity supplier and did it on the phone with just one call
i visited the water supplier and did it there and then
I changed the townhall payments, for IBI, basura etc. to my sons account, did the property registry office requirements.
There were no hic cups
Using a lawyer probably means there will be a delay so that you feel he/she had a lot of work to do, so you are happy to pay the inflated bill you will probably eventually be presented with.