My shitty revision dealer.

Basically I am currently doing exams at the moment. I always sucked at revising for tests not because I didn't want to do it but because I didn't know how to do it properly. So my friend recommended a guy who graduated my school a while ago who was a straight A student who was very smart and would sell you revision material he had from his time in our school or would go make revision sheets for the topic you needed help with as long as he knew it. At first he was really good he had quick replies and the sheets were really good and would even help talk through certain areas again if needed. However recently he just suddenly stopped responding to people unless you were trying to buy something but when you would send the money he would then just not respond again or not send the material. And it might take him over a day to respond or he might just not respond at all and half swipe your message. This genuinely sucked because he was really good when he was actually doing what he said he would do and the material and sheets he provided were all amazing. Not only that but I've sent him like 30 pounds for material I've not received and he's dodging my messages like the plague. So idek what to do here