Leaseholder didn’t send invoice now debt collectors are asking for money!

Hi, my lease ground rent has a six-monthly payment schedule, from which the leaseholder should send an invoice for the amount due. They have missed the last 2 invoices ( I haven’t received them via post) and, the first I heard about it was that the debt collection agency PDC issued a demand for the debt to be paid, plus a load of other costs, almost doubling the amount due.

I have no issue with the amount owed, but what I am not happy with is the additional costs, and the fact that I didn’t receive the invoices! I have always paid the ground rent on time, and as I was not sent these last 2 invoices, the payments were never made. Also, the leaseholder did not reach out via any alternative communication (either emails/calls/more letters) when these payments were missed, and now the debt is with PDC who are chasing me for the monies and extras!

Do I have any way of not paying the extras? I have asked PDC for proof that I received the invoices, but I am not sure what else I can do.

Does anyone have any advice, or have dealt with similar?

Thank you!

Alex