is plumbin pipe inside the wall and mold on the wall common area?

hoa send me the bill for $11,065. i think it is way over charged. i had a 3 meeting with board members. they said i have to pay everything. they can not waive the charge. they told me wall is not common area. start from beginning i told the hoa manager i will not pay one penny with their job. i told them more than 10 times before they start the job. i did not have any paper work from them such inspection report, how many days work, agreement or contract. contractor has my lock box code number. they were in and out my condo without my permision. also, manager told me i have to stop remodle process. i have to be out of my condo until they finish the job. finally they finish 30 days later. there was only one guy doing the work. he did not show up work every day. the work they did should be done within 3 days. also, i estimated material they used was no more than $300. it was just few dry wall and can of mold premier. and one day i received a bill in my mail. when i open it. it was bill for $11,065. i am new owner in this complex. i think they just bully me. may be they think i am stupid chinese guy. at this point i don't know what to do any more. hoa keep charge me late fee and interest for the balance. can you give me some advise what to do. is there any place i can go report them. all the home owners told me. it is not my responsibilty for this work. plumbing inside the wall and wall is common area. please help! please give me advise. please tell me who can help me.
thanks