Need Advice - Caddo Sect. 2-5N-12W - Urban Oil not Paying

Urban Oil & Gas Group, LLC purchased the Apache Bromide SU Tract 10 well from Bass Petroleum in 2017 (both are Texas-based companies). We have received monthly checks on this well for over 15 years, up until Bass sold to Urban. Urban has not made any payments on the well since they took it over. According to Bass, they provided their pay decks to Urban, so they should have our royalty interest. I reached out to Urban and was told that they were working on trying to determine why we have not received payment. That was in early January. Now they will not respond to emails. When I try to call, the recording says I must leave a voice message, which I do - but no response. I am assuming that the well is still producing, since I was told they were looking into why we were not being paid (as opposed to being told that the well was shut in, or being re-worked). I looked on the OCC website, but neither Bass or Urban has reported any production to the OCC (probably because they are a TX company). What can I do to get Urban to pay us our back royalties, and begin to pay us going forward? Is hiring an attorney our only option? Or should I reach out to the OCC and file a complaint (is that an option?)? Any advice would be helpful. Thanks.