write down how you'd tell me to do the same thing, in english. That is the hard part. Giving an example isn't enough. You need to spell out step by step how it should be handled, and what assumptions you are making.
Is the pattern always "letter, digit, comma" repeated some number of times? is the ellipses actually in your string, or is that just to illustrate? Can you have two letters before a number, and what does that mean?
There are other issues, but this should get you started.
There are only two hard things in computer science: cache invalidation, naming things, and off-by-one errors