Eligibility for obligation to pay (Verbintenis tot tenlasteneming)

My application for Verbintenis tot tenlasteneming (obligation to pay) for the studies of my son in college was rejected by Antwerp townhall.  They cited reason that A card holders are not eligible. But I was issued the same last year. Now this document is again needed for renewal of my sons resident card which is expiring by the last week of this month.

I checked with the following website:

https://dofi.ibz.be/nl/themes/third-country-nationals/study/favorites/verbintenis-tot-tenlasteneming .  As per this portal it seems that Non Belgians / those not having long term resident cards are also eligible, if  it is for the benefit of a relative upto 3rd degree.

The website leuven.be clearly states as following. link https://www.leuven.be/en/formal-obligation-annex-32.  The relevant text is reproduced below:

"Can you stand surety?

In order to stand surety, you must comply with one of the following conditions:

You are a Belgian.

You are an EU national residing in an EU country.

You are a non-EU national with permanent stay in Belgium or in another EU member state.

E.g. you hold a B, C/K, D/L, F(+) or M(+) card

Not if you hold a Belgian A or H card (unless you are a relative up to the third degree).

You are a non-EU relative up to the third degree (related by blood or by marriage)

In that case, you must present proof of the kinship at the Belgian embassy or at the Belgian municipality where you live (one or several birth or marriage certificates).

Read the rules on translation and legalisation of certificates. This prevents us from having to reject your documents and thereby delaying your application."

I am in Belgium since 2016, but still holding an A card.  Didnt apply for an L card as I was not paying social security until 2021.

What options are available to me now?

Please help by sharing your understanding on this.