UK Support Tel Number Simply not Working - not connecting

Trying to get in touch with Support to cancel an order (AVAP1689443755 for £54.99); followed the instructions and completed the webform. Given a case number - 24823879 - and a tel number +44-800-031-8398 which simply does not work. Have tried multiple time (on both mobile & landline) and the call does not connect.
Bottom line (& purpose of the whole support request & community post!) - I’d like a full refund of £54.99 for automated order AVAP1689443755 as I do not use the product.