This is the classic manufacturer get out.
"It's the software, guv. Nothing to do with us"
They aren't agents for Microsoft in the way you mean, I'm afraid. They install the software and assume responsibility for the support to the customer. On that basis they get it for a much reduced price. The quality of the support you can judge for yourself
I think you have three options
If you have bought an extended warranty from Mesh you can appeal to Davey on this forum and see if he will do anything to help
You can go to Trading Standards and seek their
help, or consult Citizen's Advice or a solicitor
Or you can preserve your sanity by getting a local firm or a computer literate friend to have a look at it. It may end up by costing you a few quid but the computer may be restored to working order
The help line, such as it is, appears from all accounts to be a waste of space, and the software line is a good way to empty your wallet. Don't drive yourself mad by wasting time with them