You are entitled to your opinion but opinions should at least be based on facts. Radio Cymru and S4C audiences are increasing, and many watch it online and through social media.
These are the last articles I can find, if you have other concrete evidence other than your own opinions on social media then please share and I'll gladly withdraw.
http://www.bbc.co.uk/news/uk-wales-37781547BBC Radio Cymru audience figures hit 21st Century low
http://www.bbc.co.uk/news/uk-wales-33595994S4C TV viewing figures fall in Wales
Ofcom PSB Report 2017
S4C
• In a typical week in 2016, 339,000 viewers in the S4C region watched S4C on
television for at least three consecutive minutes. This continues a steady decline in
weekly reach since 2011. The figure goes up when all viewers across the UK are
taken into account: weekly reach was 545,000 viewers in 2016, a decrease since
2015 when audience figures peaked. As S4C is a niche channel, its viewing hours
often fall outside the industry standard seven-day time-shifted window on TV. When
we include figures for viewing on the TV set between eight and 28 days after
transmission, S4C’s 2016 reach increased to 345,000 in Wales and 602,000 across
the UK.