Strange Carry On

Possession - Section 8 and Section 21

Commenced a new tenancy 6 month ago (just as Covid was happening), I credit checked new tenants, didn't come back great (lesson learnt), I said they can only have the house if they pay 6 months rent in advance. Never in a million years expecting that to happen. They paid it and six months on have not moved in. Neighbours keep me well informed. It is partly furnished (peaking through the windows), car in the garage. I've done my own digging and found out they own their own house which looks like it was being re-possessed, but Covid stopped that. They've now stopped paying the rent, won't answer my calls or messages. I've written to them and offered a surrender notice as a way out of their contractual arrangement. No response. They are still alive and kicking as they are very active on Face Book (I'm secretly stalking them). The contract has a 6 month break clause. How do I get them "out" even though they're not "in"?