Hi Albert,
Firstly I am not a solicitor so take what I say with a pinch of salt.
It appears that you are in a very tricky situation as the agreement was verbal. that said if the property was sold actually tenanted it should be easy to prove that the tenants were there during the period nov-jan (also I am sure the tenants will have proof of payments i.e. chouse).
one first step could be to instruct a solicitor to write a first letter (draft it as best you can first to reduce costs) and take it from there.
otherwise you could go down the small claims court route (no solicitors needed I think) but I do not know a great deal about this.
I am sure that despite the agreement being verbal given when ou took over the property it should be fairly clear that the monies are owed to you. the verbal agreement is still the problem as the previous owner may say was always agreed it was owed to him
Thank you
Nelson