RB not ridden in 4 years unable to shift gear
If people can figure out what the problem is, you can probably fix this yourself without needing specialist tools. Honestly, though, take it back to Halfords and get them to actually do the work you've presumably already paid them to do, because this is pretty ridiculous.

In general, I'd recommend taking bikes to a specialist bike shop rather than somewhere like Halfords: the level of clue is generally much higher and they'll actually make sure the bike is working before they hand it back to you.