It should be perfectly possible to fully close your accounts down - referred to as "baja" in Spanish. But, if you have made it clear to the utility companies that new owners are moving in, it's more usual for the new owners to contact them to switch the contracts into their names (you can't do it, because you can't authorise direct debits from someone else's bank account) in order to avoid reconnection charges, and sometimes new meter installations, inspections etc. It really is in the interest of the new owners to do this ASAP to avoid such hassle - and the utility companies probably prefer it this way too as it's less work for them.
If possible, take final readings with the new owners, and stress that they must contact the relevant companies and make the contract changes ASAP. If you are in any doubt that they will do this, you can give them a deadline - say, one week, after which you can contact the companies and cancel your services. In my experience, for this reason, buyers usually are more than happy to do the necessary within a day or two!