Bank direct debit not taken- health insurer

For past 4 months health insurer has advised each month that due to technical error on their part my dd was not taken. They then stated that total would be taken each future month. Then the technical error repeats. I am concerned that they will take large amount in June. Have I any rights ? Who is breaking the agreement to pay monthly amounts ? Any advice please

If the monthly payment is say 400 and they havn,t taken it ,they have broken the agreement.

Write to them (keep a copy) and request shortfall be added at a figure that suits you for the remaining months.eg if you can afford 200 then say that.
I expect they will do this.

Not the best but mistakes happen. Especially with SEPA which made the whole process a lot more complicated.

Any reason you couldn't make a payment in the meantime to save you getting the lump sum out in one go? E.g. By card or cheque?