The correct procedure if you cannot make contact with a frequency is normally to change back to your last frequency but tell the other frequency why and what you are doing and what frequency you are going too because they may be able to hear you. London info can phone Swansea and see what the problem is, advise you if the frequency is correct and advise you if the airfield is actually open. (CRM = use ATC)
Swansea is an Air/Ground facility so it may well be that whoever is using the radio is also involved with other duties and may not have been able to answer your call and you should not expect the same response time from A/G as from AFIS(in my opinion)
You should however have been familiar with the AIP entry for Swansea that states
[I]EGFH AD 2.22 FLIGHT PROCEDURES
1 Radio Communication Failure Procedures
(a) If a radio communications failure is experienced after establishment of RTF contact, a standard overhead joining
procedure is to be flown for the notified runway in use and circuit direction. If RTF contact has not been established,
unless an emergency is experienced which requires immediate landing, the ATZ is not to be entered, and a diversion
made to a suitable alternate aerodrome.