when I ring people they tell me there is a delay on the call

I had this issue when I was using the Three network, and I still have it using Smarty which happens to be owned by Three.  I talk to a family member on their landline, and after about 20 - 30 mins a delay builds, where the family member is not hearing what I have said for between 5-10 seconds.  They also report not hearing me for many seconds some times.  I have made these calls using bluetooth earphones, without earphones, on wifi calling and without wifi calling and the same still happens.........

I've had the same issue and it looks to be not the phones fault it could be the sim card but how would I get that fixed

What do you mean by delay? Before they hear you speak then everything is normal? Or do you mean like an old school long distance call - you say 'hello' then seconds later they hear it?

Does this happen with ALL calls? Does it happen wherever you are making the call?

Do you have a spare phone (or one you can borrow) to put in your sim and see if the same thing happens? This would rule out any phone fault.