Your TV is currently only equipped to receive analogue TV transmissions. The following analogue transmitters were permanently switched off yesterday:
Abergwynfi, Broad Haven, Bronnant, Croeserw VP, Cynwyl Elfed, Dolgellau, Duffryn, Fishguard, Glyncorrwg, Haverfordwest, Llandyfriog, Llandysul, Llangranog, Llangybi, Llwyn Onn, Mynydd Pencareg, Newport Bay, Pembroke Dock, Pencader, Preseli, Rheola, St Davids, St Dogmaels, Trefin, Tregaron, Ystumtuen.
Viewers who used to get their analogue TV reception from any of those transmitters, who wish to continue receiving terrestrial TV signal using their existing TV set, now need to purchase a Freeview set-top box. (The box simply fits between the aerial lead and the TV set).
You're outside of the intended target area for UK broadcasters. (The BBC and ITV aren't allowed to deliberately beam transmissions into the Irish Republic, because they only own the UK broadcast rights to many programmes). That means that the signal strength won't be very strong. If you were getting perfect reception of the old analogue signals there's quite a good chance that you'll be able to get decent Freeview reception, but there can be no guarantees.
In the UK, cheap Freeview boxes are available in all of the big supermarkets. They're probably also available from similar outlets in your part of Ireland (because, as your post indicates, many Irish viewers watch British TV) even though 'officially' you shouldn't be able to watch British TV channels. Otherwise you can buy one online for around €20.
You might need to upgrade your TV aerial (although the fact that you were receiving British analogue signals suggests that it's quite a good aerial anyway) and/or add a cheap signal amplifier. However you might well find that simply getting hold of a Freeview box will solve your problem.
You can't expect your landlord to pay towards any changes since 'officially' you shoul