Tax on pensions in France

Has anyone else come across this.

We get a state pension and government nhs pension from England, we filled in tax form last year, took it to tax office where it was checked and we were told we had no tax to pay.

In November last year we received letter asking for copy of S1 E121 as retired which we sent back, we also had attached copy to original tax form!

We received letter from Tax Habitation 2 weeks ago stating we had none to pay as tax office had notified them saying we were under the limit for tax.

Yesterday we received a letter from tax office stating they were now thinking of taxing us over 1000euro as they may have made an error.

Yes I have replied with copies of Pensions from England and showing tax at source on government pensions but don't understand why.

Anyone with any idea's please.

Have asked for meeting with their translator to clarify but any help appreciated as we only get these pensions and have no other income and thought we would also have a set level of tax allowance before paying tax.