Sellers information on boundaries

Title deeds of old cottages do not have any T markings to say who’s responsible for boundary fencing.
the original owner who sold it to me also owned the property next door.
he brought as a whole lot  the pair of semi detached cottage with no divided gardens. He
Renovated no.44 inserted a division of the garden and then sold it. 
he moved into the other side no.46 renovated it and then sold it to us.
in his sellers information he stated that all the boundaries between the 2 cottages were the responsibility of no. 44.
no.44 has now been sold on and they are disputing responsibility of the fences between the 2 properties and are saying that as they put up a new fence at the front boundary we should pay to replace a rear garden fence that has fallen down .
it seems their seller (who brought property from our seller) has stated shared boundaries.
i can’t understand why when given my seller divided up the garden they will not accept that he gave them responsibility!
is this worth taking up legally? Would it stand up in court? 

Sharon - it is not unusual for there to be 'mixed' understandings/views re such matters. But very much a question to seek legal advice upon with regards what might stand up in court, if it went that far, or not. 
In my experience the best way to resolve matters is through discussion and compromise where possible. But so much often depends on not only understanding and principles but also how neighbours interact/have behaved re other matters also.