Let down by Landlord Action

Possession - Section 8 and Section 21

We have a bad tenant who has not paid rent in over 6 months. We relied on Landlord action who initially issued the tenant with a section 8 and section 21. At expiry of the notices Landlord Action then progressed to the next stage and applied to the court for possion order. This turned out to be unsuccessful.
Landlord action now suggest to re-issuing a section 8 and attempt to obtain a possession order based on that.
We are struggling with making further payments to Landlord Action and the fact that this would invlove more time spent going via them, is very depressing as well as financially damaging.

Can we pursue with the section 8 ourselves?

Also, it states in our tenancy agreement that a month in advance of £550 is agreed. This however was never paid yet still, Landlord Action are adamant that it is seen as a deposit has been taken.
Can this be clrified?

Look forward to your response.
Regards
Raj Sharma