Thank you for all the great information. It sounds like Simba is a true fighter. I have nothing to do with billing this is all handled by Justanswer, I am simply an independent consultant. I will be happy to forward you over to their customer service once we are finished and they can direct you on the billing information.
From what you have described their could be a number of things going on here.
If he has not had recent blood work ( meaning in the last 3-6 months) then this has to be the first step since he is also urinating more frequently.
What we would want to look at is his current glucose levels and his kidney values. Kidney disease is by far the number one problem we see in senior cats and this will often cause inappropriate urination.
Now the fact that he is also defecating out of the box is also a key bit of information. More then 70% of cats over the age of 15 will begin to suffer from a condition called Feline Cognitive Dysfunction. This is similar to Dementia/senility in humans and not using the litter box is one of the more common symptoms. I am going to give you a link that goes over this in more detail. LINK
We also have to look at things like arthritis in a senior cat that make it difficult for them to get in and out of the box.
There are a few things we can try but a vet visit really has to be in the top of the list.
Cleaning the areas as you have been doing is very important. Look at the urineoff website to see if you recognize the bottle as something you have used in the past. If not give this a try. We have tried every product on the market for the clinic and urineoff is by far the best product we have found for removing and breaking down urine enzymes. This is guaranteed so if it does not work they will refund your money LINK
Try getting a litter box with a low opening such as this one LINK
If he is going on the carpet I would also put a box out with just a carpet remnant in it. You can get this small pieces of carpet at most dollar trees or even check with your local carpet supply store as they often just throw away small ends of carpet. Bath rugs can work too and are washable. I know not the optimum idea but much better then him going on your home carpet.
When all else fails with senior cats we often have to get something such as a closed puppy play yard leaving the cat in there when they can not be watched. These are large enough that he would have plenty of room for food , water, litter box, bed toys etc. Here is one we often suggest for our clients. Wow this a great price as well LINK
I hope this helps give you some options to try after making sure this is not due to a medical condition ( which I really suspect it is). Please reply back if you have additional questions and I will be happy to continue. If all of your questions have been answered please take a few minutes to provide a rating so I am recognized by justanswer for assisting you. Also please let me know when so that I can forward you over to customer service to discuss billing.