There have been thousands of complaints about errors in the E111 card - spelling mistakes in the surname ('Cool' instead of 'Cook', for example, or '1935' instead of '1985' in the date of birth).
The problem stems from the scanning system used to interpret handwritten application forms. If you have lousy handwriting, or use a scratchy pen, chances are you could be issued with a duff card.
And that could cause major problems if you need to use your EHIC in a medical emergency abroad - you could be refused treatment if your card details don't match up with what's on your passport.
If your card details are wrong, return it immediately. Allow 7 days for the new one to arrive, If you apply at the Post Office you can expect to wait longer - 3 weeks. By telephone 10 days.
It is quicker to do it online at
https://www.ehic.org.uk/Internet/home.do