Bad Phone Experience

My mother got the S24 FE from freedom mobile and the phone call quality is real bad. Now a call service is using the Freedom service so I can except that being not great as they don't live in a big city, but now when we try calling on WhatsApp, which uses data, the calls are cutting out too and sound just as bad. Any ideas?

Is this a Phone service issue, Freedom Mobile, or is it a phone type issue, S24fe and is there anything I can do to fix or check.