Need Help/Advice Please.

Hi. I left my wife 6 years ago. We have 2 children together. The first few months were great terms of contact with my them. Then slowly contact became less and less. She is now remarried and has another child and since then contact has become painfully minimal. As of the date of me writing this I have seen my children TWICE since Christmas. When we first split up we made an agreement that I would be able to have them for thr day..every Sunday. I do work every weekend every other month so I asked that on the month I work weekends can I see them on another day and that was also agreed. NOTHING. I don't get told never mind invited to any of their activities..including school meetings etc. I'm not told how they are doing in school. Nothing! My son who is 7 plays for a football team..I've been asking his mother for MONTHS to let me know where he's playing next and I'll come and watch and support..NOTHING. so I took it upon myself to contact his one of his coaches and tell me where they are playing next weekend..only to be told my sons mother has contacted the club and asked that no information is shared with me about my sons football games. I can honestly say..hand on heart I have NEVER done anything to merit this from her. Yes I left her..the hardest part of that was leaving the children and I suffered with severe depression for almost 2 years because of it. All I've ever done since then is want and try to see my children! I'm sure there's people here who are and have dealt with this situation or similar and I would like some advice on what actions I can take. Thank you for taking the time to read this.