The following may be useful as a method of looking your NHS number – https://www.nhs.uk/nhs-services/online-services/find-nhs-number/?fbclid=IwAR0-xS0C2pTwNtAnt5RyjWWxwDT5nn7qH8XHODrS4QPFYUwXqDVPH51_-34
The system will ask you to confirm some details (name, date of birth) and will then text your NHS Number on the mobile number registered to your GP record.