I have inserted a part of the WT band descriptors - something which is freely available for the general public. Please find the link below:
Study the mistakes which get you a Band 5. And it will become quite clear to you that format is only one of the criteria that you need to satisfy. Most probably you are making one or more of the following errors:
Being repetitive - you know, the -‘yesterday I saw a saw which could not saw’-type. Or, maybe, ‘…of the total number of students in the school, the students who played football are significantly more in number than the students who played hockey while the students who played table tennis were the least number of students. (phew!)
Making too many basic errors too frequently - affects intelligibility and coherence. The examiner will be unable to understand what exactly you mean to say. A 5–5.5 band paper once corrected looks something like what I have attached. It is an essay and not a graph/chart. But the same principles apply here too.
Not completing the required task/s - discuss 2 sides and give your opinion. Maybe you did not give your opinion? Mention the important points, summarise, and compare where necessary. Maybe you forgot to do one of them? Or could it be that you read the question completely wrongly and your response went off-track from the word go?
Inability to use more than a very simple sentence structure - examine the language below. Coherence is affected. The structure is not only wrong but also very simple. Whenever an attempt is made to write complex sentences, it leads to problems. This is typical of below 6 band writing:
WT1 and/or WT2 significantly short in length - this is also another no-no. Although not specifically mentioned in the band descriptors that are available to the public, experience has taught us this valuable lesson. Not me alone, Elizabeth of IELTS Preparation: Free Tips, Lessons & English fame says the same thing. Ditto, ielts-simon.com.
Frankly, go to them and ask them if there is anything else, in addition, which you may try to adopt or avoid in order to get out of your current situation. My guess is, they will ask you to stick to the basics of writing and to do exactly those things which will help in making your response clear, concise, and relevant - all without repetition.
Hope I have been of some help - to you and to all those who are facing a similar problem as yours.