You don't say what country you are in. I'm in the UK, and this applies here.
In terms of "extending without telling you", by allowing you to continue to show up for work, they are telling you they are happy to continue on the same basis (unless extending the contract on different terms was written into the original contract). By continuing to show up, you are saying you are also happy with that.
In England the courts will say that there is an "implied variation" of the original contract, i.e. that both parties have implicitly agreed to change the end date of the contract. The rest of the contract applies, (with any necessary changes implied by the changed end date).
About your bonus. The position of an independent contractor is different to that of an employee. They pay you more because they value the flexibility of being able to get rid of you if they no longer need your special skills. You become a contractor because you have confidence in your marketability and don't wish to trade lower rates for job security.
Employees on the other hand receive bonuses on complex vesting and claw-back schemes where they may be awarded a bonus in July, but won't recieve it until December, but if they leave before next July they must repay it, by which time their next bonus is announced...
If you feel you are worth 10% more money, you should simply tell them that. Say "I am really happy to continue working for you on the same basis, but what with the market position and cost of living, I have to put up my rates by 10% starting next month". or: "I really enjoy working here, but I need charge a rate which is closer to what I could get elsewhere".
The crucial points when negotiating are:
What is the value to the client of the work you are doing? If getting the job done costs more than the value it provides, they will simply hire nobody to do the job, and the job will not be done.
What would it cost them to hire somebody else? If they can get the job done for less by somebody else (i.e. taking into account productivity) they will.
Both those factors create a maximum you can charge, so you can't really ask for more than the lower of those two. In reality the second factor - market rates - is likely to be the crucial one. As an independent contractor you should always know what the market rate is. In the UK you can trawl JobServe to get a good idea what the market rate for any skill is - and also what skills it might be worth learning!