iphone 12 mini has poor sound quality on calls, is this 'normal'?

i've just got an iphone 12 mini and the phone calls sound like an old CB radio, harsh, muffled, distorted. it does not appear to be the speaker as i can use skype test call and it sounds fine, just seems like the cellular voice calls. I have tried two different providers/SIMs and its the same.

is this an issue for all these models? just some maybe? it's so bad i'm looking to return the phone, my iphone 8 i upgraded from was crystal clear.

i'd appreciate any reports back from the field :)