PLEASE HELP: Issues with former Landlord (Brussels)

Dear Internations members,

I am reaching out to you to see if one of you has any recommendation or could offer some guidance on the following issues i have with my former Landlord.

In December Protected content moved to a flat Protected content . the rent was Protected content Protected content charges (charges being hot water, heating, and concierge).
Within 3 months i have received a bill for Water of Protected content , which i apparently used extra.
I was schocked as within those 3 months i was travelling at least one month.
For this, and some other personal reasons i asked to leave the appartment end of July, even though my contract didnt allow me. The landlord said i could leave, if i find someone to replace me, which i did.

In November Protected content , now i received another letter from that landlord stating that i owe him Protected content , a calculation apparently made by the syndic, for the usage of extra heating maintenance and so on( documents r very complciated to understand).

Again i am shocked as there is no way i consumed soo much in this appartment, especially only staying 6 months in total!!! i have moved a couple of times, but NEVER received such bills.

Now the owner is threatening me with suing me, and doesnt want to give my deposit back.

I find it really not normal, that when i break down everything by month, that my charges are actually exceeding the rent?? Could i do something on that?

Also when i signed the contract the landlord signed the contract, mentioning it was from October Protected content of December, to avoid doing the electricity effeciency test, which is required by Belgium law since Oct Protected content . Could it be that he knew there is sth wrong and thats why he recommended not to do it?

Is there any way for me to check if he registered with the comune that he rented his appartment? I was told if he didnt register the appartment with the commune, the contract is not valid?

Do you know if i can get any affordable legal advice? i just left my job for my own start up and i really can not afford to pay a llawyer now?

Any help is greatly appreciated!! Thanks everyone and have a great rest of the weekend!!!

Cheers,
Ozan