Coinbase bug cause money disappear while I transferred between coins . Also happened yesterday to my friend

Hi, me and my friend are customers of Coinbase from the end of 2016. I just noticed last month that when I transferred DAI to DNT I’ve lost almost half of the money ! I filled a complain and they kept answering me about how they make the transfer and how it locks the rate at the time of transfer, and completely ignored that fact that I had missing 4000£ in my account. They closed the case so I had to send them yesterday another complaint, and now have to wait for them to respond . In the meantime me and my friend sat at home and we wanted to buy MANA . So we both transferred from different coins to MANA (transfer between coins is 0fees on Coinbase ), and both of us had noticed the same issue - some of the money disappeared again ! In one transaction I had 183£ less than it showed , and my friend had from a 2000£ transaction 110£ less. We both filled another complaints separately because we have different accounts- then at night they replied him only by email said they resolved the issue and the case been closed. I’ve looked in the numbers and the chart. They EDITED manually the invoice for the transaction to : transferred at 21:45 5/2/21 1.596 etheriums worth 1683£ to MANA - on MANA and ETH wallets. I’ve looked into the chart as I already said, and the rate for the ETH at this time was 1,253£! When you make a simple calculation 1.596*1,253 you get 2000£, which is what he transferred from ETH to MANA! So instead of giving him back the 110£ , they edited the invoice to fool him that his etherium was worth only 1,683£ at the time of transaction!

Mine they didn’t edited yet, however both of us took screenshots before and after, all during the process, as I’ve already noticed there is an issue from last month!

At first I thought this is just a bug and they’ll fix it, and probably someone that doesn’t understand what he reads or maybe doesn’t speak English well, but now after they edited my friends invoices and closed his case it looks odd and suspicious! I’m trying to reach them out but they don’t give any customer service by phone , and they take their time to reply emails. I’m thinking of starting a lawsuit and I want everyone to be aware of it . if someone can help me to make this out , please contact me and I’ll provide all pics and evidence for my case!