How can I get in touch with Qatar in the UK

you need to change within this, you won’t incur any penalties or fees.
Can you Change your ticket on United ?
Yes, you can reschedule United flight. However, you may need to pay a change fee depending on the airline you booked with and the fare class of your ticket.

Source: https://developer-community.sage.com/topic/5505-help~number%E2%84%A2%E2%84%A2how-can-i-get-in-touch-with-qatar-in-the-ukdont-fear-iam-here%E2%84%A2/