Yes, you can defend yourself of this charge, but it likely requires one of your friends to fall on the sword for you. I don't know how willing they will be to do that. Of equal concern is the fact that your lawyer is not returning your calls. That is very troublesome. The Rules of Professional Conduct requires an attorney to be diligent in keeping the client informed and I have read a number of disciplinary notices about attorneys who did not return calls. You need to get that problem...
The simple answer is "hell yes" you should challenge this. ETG tests have many, many flaws to them. In fact the US Dept. of Health issued an advisory to probation departments a few years ago stating that they should not rely on ETG tests in probation revocation hearings. A simple Google search on ETG testing will provide you with a ton of information about many of the fallacies of this testing process.
That will depend on the jurisdiction. Many people are struggling to pay fines right now due to current economic conditions. I would really consult with a local attorney before you make this request. The court might be willing to give you more time if the circumstances warrant it. You also might want to see what kind of facility you would serve your time at. It might be worth taking a little more time to pay off the fines.
You need to contact a local attorney immediately. In my jurisdiction, certain exceptions can be made due to hardships or other factors that makes it impossible to comply with a SCRAM order. This will also depend on whether or not this is a pre-trial condition of your release, or a condition of your sentence. Contact a local lawyer now.
In some States, Washington for example, you may be able to avail yourself of the affirmative defense of "safely off the roadway." Whether Texas recognizes that is a question for a top notch Texas DUI attorney. However, the purpose of this affirmative defense is to encourage people to do exactly what you did by realizing that you were in no condition to drive and then doing the right thing by not driving.