Unable to dial two numbers from Echo

Heya! I have set up 4 x new Amazon Echos for my Mum. They all appear to be working except for one issue - it won’t call my number or my husband’s number. We both have iPhone 16s but that’s the only thing I can think of. It doesn’t have an issue calling any other number in the address book, just these two numbers. Has anyone come across this issue before? Many thanks.