What number can I call from UK to help me connect my MacBook to the internet?

Official Apple help may be found through Get Support

https://getsupport.apple.com/

Or an Apple Genius page may route in your region.

• Genius Bar Reservation and Apple Support Options - Apple

https://www.apple.com/retail/geniusbar/

There may be other help in official Apple site pages, such as this:

• My Support - Official Apple Support

https://support.apple.com/my-support

This likely has an inner component to direct you to regional help.

There are phone numbers that take one to retail or corporate yet..

..I've no way of knowing which ones do what, if anything at all..

Due to nature of this 'Volunteer' user-to-user help discussion.

Contact - How to Contact Us - Apple (UK)

https://www.apple.com/uk/contact/

"For other enquiries, contact Apple

Store Customer Service on 0800 048 0408. Lines are open Monday-Friday

08:00-20:00 and Saturday-Sunday 09:00-18:00. Shop with SignTime BSL"

From UK site above:

Contact Apple Support

Need service or support? Start your request online and we’ll find you a solution.

More ways to get help:

• Contact iTunes Store support
• Technical support: 0800 107 6285
• See all worldwide support telephone numbers
• Contact a network provider
• Make an appointment at an Apple Retail Store Genius Bar
• Find an Apple Authorised Service Provider
• Beats support:
• 0800 028 2329 or see all worldwide support telephone numbers

Sorry to hear your having trouble connecting your MacBook to internet. I assume you have a local internet provider. You should be able to do this yourself.Connect to the internet with your Mac - Apple Support If this is not working then use the links K Shaffer provided. Someone can then walk you through it.

MacBooks were discontinued 3 years ago.