Absolute 80s (together with Planet Radio and Premier Christian Radio) has opted to use the cheaper broadcast service being offered by the new Sound Digital multiplexes. They don't cover all of the country though, so many people will lose reception of Absolute 80s when the station is removed from the existing multiplex after 4th April. It seems likely that you're one of them.
See here for further explanation:
http://www.a516digital.com/2016/02/faq-dab-digital-radio-changes.html
See here for (a photograph of) a map of the Sound Digital multiplexes:
https://pbs.twimg.com/media/CP_MYu6WcAAZJX3.jpg:large
(That seems to be the best map that's currently available).
Check here to see which stations you should now expect to be able to receive:
http://www.getdigitalradio.com/whats-on-dab/at-your-address/
Absolute 80s isn't available via Freeview but if you've got satellite TV it's on Sky channel 0200 or Freesat channel. If you've got cable it's on Virgin Media channel 951. You can also receive it using internet radio sets or by clicking on 'Listen Live' here:
http://absoluteradio.co.uk/80s/
Planet Rock also isn't on Freeview bit it's available on satellite (Sky 0110, Freesat 730) or cable (Virgin Media 924). It's also available through internet radio or from here:
http://radioplayer.planetrock.com/live/